Allow 2.X and 3.X to coexist. Includes are now stored under
/usr/include/fuse3 and library is named libfuse3.*. Invoke pkg-config with
"fuse3" as the first argument to build with version 3 of the library.
If the "fsname=" option contained a comma then the option parser in
fusermount was confused (Novell bugzilla #641480). Fix by escaping
commas when passing them over to fusermount.
Reported by Jan Engelhardt
