Fixes on pkg-config leakage (#59)

* Fix on space leakage of pkg-config.
As PKG_CONFIG_PATH adds paths to pkg-config, modify such env leads
some autotols detect base system packages.
Replace with PKG_CONFIG_LIBDIR.

* Small fixes:
GHscripts/setup: Remove unnecessary qemu variants. Add flex as
		 gcc requires it.
editor/nano: Fix ncursesw detection.
gui/SDL2: autotools will try to use /usr/X11 /usr/X11R...
	  unconditionally. Try specify hard coded X paths.
	  Remove sysctlbyname detection from configure.
lib/libpng: Correct libz prefix to _Cz_.
lib/readline: Patch readline.pc to give -ltinfo instead of
	      relies on tinfo.pc which won't present.
	      This influences python configure.