Do not clobber PKG_CONFIG_PATH during configure.

--- HandBrake-0.10.5/gtk/module.rules.orig	2016-02-11 14:14:05.000000000 -0600
+++ HandBrake-0.10.5/gtk/module.rules	2016-10-29 22:27:50.550960848 -0500
@@ -15,7 +15,7 @@
 	set -e; cd $(GTK.src/); NOCONFIGURE=1 ./autogen.sh
 	set -e; cd $(GTK.build/); $(call fn.ABSOLUTE,$(GTK.src/))configure \
 		$(GTK.CONFIGURE.extra) \
-		PKG_CONFIG_PATH=$(BUILD/)contrib/lib/pkgconfig \
+		PKG_CONFIG_PATH=$(BUILD/)contrib/lib/pkgconfig$(if $(PKG_CONFIG_PATH),:)$(PKG_CONFIG_PATH) \
 	    CFLAGS="$(call fn.ARGS,GTK.GCC,.g .O *D ?extra)" \
 	    LDFLAGS="$(call fn.ARGS,GTK.GCC,?strip .g .O ?extra.exe)" \
 	    --prefix=$(PREFIX) \
--- Handbrake-0.10.5-0.77d09e9-checkout/make/include/contrib.defs	1969-12-31 18:00:00.000000000 -0600
+++ Handbrake-0.10.5-0.77d09e9-checkout/make/include/contrib.defs	2016-11-01 13:11:43.826144311 -0500
@@ -119,7 +119,7 @@
     endif
     $(1).CONFIGURE.env.CPPFLAGS = CPPFLAGS="-I$$(call fn.ABSOLUTE,$(CONTRIB.build/))include $$(call fn.ARGS,$(1).GCC,*archs *sysroot *minver ?extra *D)"
     $(1).CONFIGURE.env.LDFLAGS  = LDFLAGS="-L$$(call fn.ABSOLUTE,$(CONTRIB.build/))lib $$(call fn.ARGS,$(1).GCC,*archs *sysroot *minver ?extra.exe *D)"
-    $(1).CONFIGURE.env.PKG_CONFIG_PATH  = PKG_CONFIG_PATH="$$(call fn.ABSOLUTE,$$(CONTRIB.build/))lib/pkgconfig"
+    $(1).CONFIGURE.env.PKG_CONFIG_PATH  = PKG_CONFIG_PATH="$$(call fn.ABSOLUTE,$$(CONTRIB.build/))lib/pkgconfig$(if $(PKG_CONFIG_PATH),:)$(PKG_CONFIG_PATH)"
 
     $(1).CONFIGURE.env.args = !CC !CFLAGS !CXX !CXXFLAGS !CPPFLAGS !LD !LDFLAGS !PKG_CONFIG_PATH !LOCAL_PATH !CROSS
     $(1).CONFIGURE.env = $$(call fn.ARGS,$(1).CONFIGURE.env,$$($(1).CONFIGURE.env.args))