Changes language for Geeqie's source files from C to C++ by renaming 'src/**.c' files...

Changes language for Geeqie's source files from C to C++ by renaming 'src/**.c' files to 'src/**.cc'.

commit auto-generated with:
$for file in $(find src/ -type f -iname '*.c'); do ccfile=$(echo "$file" | sed -e 's#\.c$#.cc#'); git mv -- "$file" "$ccfile"; done