configure, plug-ins: make libpng a hard dependency

configure.ac

@@ -1282,27 +1282,10 @@ AC_SUBST(GS_LIBS)
 # Check for libpng
 ##################
 
-AC_ARG_WITH(libpng,  [  --without-libpng        build without PNG support])
+PKG_CHECK_MODULES(PNG, libpng >= libpng_required_version)
 
-have_libpng=no
-if test "x$with_libpng" != xno; then
-  have_libpng=yes
-  PKG_CHECK_MODULES(PNG, libpng >= libpng_required_version,
-    FILE_PNG='file-png$(EXEEXT)',
-    [have_libpng="no (libpng not found)"
-     AC_MSG_ERROR([
-*** Checks for PNG library failed. You can build without it by passing
-*** --without-libpng to configure but you won't be able to use PNGs then.])])
-fi
-
-if test "x$have_libpng" = xyes; then
-  MIME_TYPES="$MIME_TYPES;image/png;image/x-icon"
-  PNG_CFLAGS="$PNG_CFLAGS -DPNG_PEDANTIC_WARNINGS"
-fi
-
-AC_SUBST(FILE_PNG)
-
-AM_CONDITIONAL(HAVE_PNG, test "x$have_libpng" = xyes)
+MIME_TYPES="$MIME_TYPES;image/png;image/x-icon"
+PNG_CFLAGS="$PNG_CFLAGS -DPNG_PEDANTIC_WARNINGS"
 
 
 ##################
@@ -2370,7 +2353,6 @@ Optional Plug-Ins:
   OpenEXR:             $have_openexr
   PDF (import):        $have_poppler
   PDF (export):        $have_cairo_pdf
-  PNG:                 $have_libpng
   Print:               $enable_print
   PSP:                 $have_zlib
   Python:              $enable_python

plug-ins/Makefile.am

@@ -37,10 +37,6 @@ endif
 endif
 endif
 
-if HAVE_PNG
-file_ico = file-ico
-endif
-
 if OS_WIN32
 twain = twain
 win_snap = win-snap
@@ -61,7 +57,7 @@ SUBDIRS = \
 	file-faxg3		\
 	file-fits		\
 	file-fli		\
-	$(file_ico)		\
+	file-ico		\
 	$(file_jpeg)		\
 	$(file_psd)		\
 	file-sgi		\

plug-ins/common/Makefile.am

@@ -103,7 +103,7 @@ libexec_PROGRAMS = \
 	$(FILE_PDF_LOAD) \
 	$(FILE_PDF_SAVE) \
 	file-pix \
-	$(FILE_PNG) \
+	file-png \
 	file-pnm \
 	$(FILE_PS) \
 	$(FILE_PSP) \
@@ -175,7 +175,6 @@ EXTRA_PROGRAMS = \
 	file-mng \
 	file-pdf-load \
 	file-pdf-save \
-	file-png \
 	file-ps \
 	file-psp \
 	file-svg \

plug-ins/common/plugin-defs.pl

@@ -56,7 +56,7 @@
     'file-pat' => { ui => 1, gegl => 1 },
     'file-pcx' => { ui => 1, gegl => 1 },
     'file-pix' => { ui => 1, gegl => 1 },
-    'file-png' => { ui => 1, gegl => 1, optional => 1, libs => 'PNG_LIBS', cflags => 'PNG_CFLAGS' },
+    'file-png' => { ui => 1, gegl => 1, libs => 'PNG_LIBS', cflags => 'PNG_CFLAGS' },
     'file-pnm' => { ui => 1, gegl => 1 },
     'file-pdf-load' => { ui => 1, optional => 1, libs => 'POPPLER_LIBS', cflags => 'POPPLER_CFLAGS' },
     'file-pdf-save' => { ui => 1, gegl => 1, optional => 1, libs => 'CAIRO_PDF_LIBS', cflags => 'CAIRO_PDF_CFLAGS' },