dav: Set the is_hidden property for files starting with a '.'

https://bugzilla.gnome.org/show_bug.cgi?id=720275
Convert libdaemon to a private shared library

Convert libdaemon to be a private shared library called libgvfsdaemon,
much like libgvfscommon.  It has the benefit of reducing the binary
size of each daemon by between 100 and 200KB and reduces the memory
footprint if using several backends at the same time.

https://bugzilla.gnome.org/show_bug.cgi?id=561187
Convert libgvfscommon to a private shared library

Convert libgvfscommon to a private shared library since it is not used
by anything outside of the libdir.  Also, don't version it.

https://bugzilla.gnome.org/show_bug.cgi?id=561187