Ignore the 'config.cache' file

Created by './configure -C' (or './autogen.sh -C') which many
people just run as an old habit.

Author: vpodzime

.gitignore

@@ -6,6 +6,7 @@ stamp-h1
 /autom4te.cache
 /compile
 /config.guess
+/config.cache
 /config.log
 /config.status
 /config.sub