support regex and co in 'apt-cache policy $pkg' again

Regression of 1e064088bf7b3e29cd36d30760fb3e4143a1a49a (1.1~exp4) which
moved code around and renamed methods heavily ending up calling the
wrong method matching packagenames only instead of calling the full
array. Most commands work with versions, so this managed to fly under
the radar for quite a while.

Closes: 807870

apt-pkg/cacheset.cc

@@ -336,7 +336,7 @@ bool CacheSetHelper::PackageFromString(PackageContainerInterface * const pci, pk
 bool CacheSetHelper::PackageFromCommandLine(PackageContainerInterface * const pci, pkgCacheFile &Cache, const char **cmdline) {
 	bool found = false;
 	for (const char **I = cmdline; *I != 0; ++I)
-		found |= PackageFrom(CacheSetHelper::PACKAGENAME, pci, Cache, *I);
+		found |= PackageFrom(CacheSetHelper::STRING, pci, Cache, *I);
 	return found;
 }
 									/*}}}*/

test/integration/test-policy-pinning

@@ -83,6 +83,15 @@ buildsimplenativepackage "coolstuff" "all" "2.0~bpo1" "backports"
 
 setupaptarchive
 
+testsuccessequal "coolstuff:
+  Installed: (none)
+  Candidate: 2.0~bpo1
+  Version table:
+     2.0~bpo1 500
+        500 file:${APTARCHIVE} backports/main all Packages
+     1.0 500
+        500 file:${APTARCHIVE} stable/main all Packages" apt policy '^cool.*'
+
 testequalpolicycoolstuff() {
 	local INSTALLED="${1:-(none)}"
 	local CANDIDATE="${2:-(none)}"