dselect: Parse the system curses.h header instead of dselect-curses.h

Regression introduced in commit 51926eebbba1f20c3bf994e7364512a1c63a25f2.

Because our local header file that decides which curses header to
include also matches on curses.h, we've been processing that header all
this time, meaning we've defaulted to the builtin and override keys only.

debian/changelog

@@ -24,6 +24,9 @@ dpkg (1.17.14) UNRELEASED; urgency=low
   * Stop warning on unknown arbitrary fields from dpkg-deb.
   * Remove unnecessary handling of obsolete Package_Revision field in dselect
     ftp method.
+  * Fix the build system to parse the system curses.h header instead of
+    dselect-curses.h, to not just default on the builtin and override keys
+    for dselect key bindings support. Regression introduced in dpkg 1.15.1.
 
   [ Raphaël Hertzog ]
   * Explain better in deb-triggers(5) why interest/activate-noawait should be

dselect/Makefile.am

@@ -55,7 +55,7 @@ curkeys.$(OBJEXT): curkeys.h
 curkeys.h: $(srcdir)/keyoverride $(srcdir)/mkcurkeys.pl
 	$(AM_V_GEN) cursesfile=`echo '#include "dselect-curses.h"' | \
 		$(CPP) $(CPPFLAGS) -I$(top_builddir) -I $(srcdir) - | \
-		grep 'curses.h' | head -n 1 | \
+		grep '[^-]curses\.h' | head -n 1 | \
 		sed -e 's/^[^"]*"//; s/".*$$//'`; \
 	if [ "$$cursesfile" = "" ]; then \
 		echo "can't find curses file"; exit 1; \