libdpkg: Move field names from parse errors to arguments

Try to generalize the error strings so that they get coalesced when
marked for translation, or are usable by other fields in the future.
This also makes sure no translator will accidentally translate field
names.

lib/dpkg/fields.c

@@ -218,7 +218,8 @@ f_status(struct pkginfo *pkg, struct pkgbin *pkgbin,
 {
   if (ps->flags & pdb_rejectstatus)
     parse_error(ps,
-                _("value for 'Status' field not allowed in this context"));
+                _("value for '%s' field not allowed in this context"),
+                "Status");
   if (ps->flags & pdb_recordavailable)
     return;
 
@@ -236,7 +237,8 @@ f_version(struct pkginfo *pkg, struct pkgbin *pkgbin,
           const char *value, const struct fieldinfo *fip)
 {
   parse_db_version(ps, &pkgbin->version, value,
-                   _("error in Version string '%.250s'"), value);
+                   _("error in '%s' field string '%.250s'"),
+                   "Version", value);
 }
 
 void
@@ -247,7 +249,8 @@ f_revision(struct pkginfo *pkg, struct pkgbin *pkgbin,
   char *newversion;
 
   parse_warn(ps,
-             _("obsolete `Revision' or `Package-Revision' field used"));
+             _("obsolete '%s' or '%s' field used"),
+             "Revision", "Package-Revision");
   if (!*value) return;
   if (str_is_set(pkgbin->version.revision)) {
     newversion = nfmalloc(strlen(pkgbin->version.version) +
@@ -266,12 +269,14 @@ f_configversion(struct pkginfo *pkg, struct pkgbin *pkgbin,
 {
   if (ps->flags & pdb_rejectstatus)
     parse_error(ps,
-                _("value for 'Config-Version' field not allowed in this context"));
+                _("value for '%s' field not allowed in this context"),
+                "Config-Version");
   if (ps->flags & pdb_recordavailable)
     return;
 
   parse_db_version(ps, &pkg->configversion, value,
-                   _("error in Config-Version string '%.250s'"), value);
+                   _("error in '%s' field string '%.250s'"),
+                   "Config-Version", value);
 
 }
 
@@ -297,8 +302,8 @@ static void conffvalue_lastword(const char *value, const char *from,
 
 malformed:
   parse_error(ps,
-              _("value for 'Conffiles' field has malformatted line '%.*s'"),
-              (int)min(endent - value, 250), value);
+              _("value for '%s' field has malformatted line '%.*s'"),
+              "Conffiles", (int)min(endent - value, 250), value);
 }
 
 void
@@ -319,8 +324,8 @@ f_conffiles(struct pkginfo *pkg, struct pkgbin *pkgbin,
     if (c == '\n') continue;
     if (c != ' ')
       parse_error(ps,
-                  _("value for 'Conffiles' has line starting with non-space '%c'"),
-                  c);
+                  _("value for '%s' has line starting with non-space '%c'"),
+                  "Conffiles", c);
     for (endent = value; (c = *endent) != '\0' && c != '\n'; endent++) ;
     conffvalue_lastword(value, endent, endent,
 			&hashstart, &hashlen, &endfn,
@@ -507,7 +512,8 @@ f_dependency(struct pkginfo *pkg, struct pkgbin *pkgbin,
         }
         if ((dop->verrel != dpkg_relation_eq) && (fip->integer == dep_provides))
           parse_warn(ps,
-                     _("Only exact versions may be used for Provides"));
+                     _("Only exact versions may be used for '%s' field"),
+                     "Provides");
 
         if (!isspace(*p) && !isalnum(*p)) {
           parse_warn(ps,
@@ -613,8 +619,8 @@ f_trigpend(struct pkginfo *pend, struct pkgbin *pkgbin,
 
   if (ps->flags & pdb_rejectstatus)
     parse_error(ps,
-                _("value for 'Triggers-Pending' field not allowed in "
-                  "this context"));
+                _("value for '%s' field not allowed in this context"),
+                "Triggers-Pending");
 
   while ((word = scan_word(&value))) {
     emsg = trig_name_is_illegal(word);
@@ -638,8 +644,8 @@ f_trigaw(struct pkginfo *aw, struct pkgbin *pkgbin,
 
   if (ps->flags & pdb_rejectstatus)
     parse_error(ps,
-                _("value for 'Triggers-Awaited' field not allowed in "
-                  "this context"));
+                _("value for '%s' field not allowed in this context"),
+                "Triggers-Awaited");
 
   while ((word = scan_word(&value))) {
     struct dpkg_error err;