Resolve library names to shared libraries ourselves

Resolve library names to shared libraries ourselves

Using ctypes.util.find_library() to resolve library names to
sonames causes problems with dealing with uninstalled libtool
operation properly. We're unlikely to find any way of combining
the two that will be robust against future changes in both
facilities.

Switch to a different approach - run 'ldd' on the compiled
introspection binary and extract sonames from there This is
less portable but should be quite robust where it works.

utils.py dumper.py: Move libtool-command-line finding into utils.py
girwriter.py: Remove library name resolution from here, expect libraries
  to be passed in preresolved.
shlibs.py scannermain.py: New file including resolve_shlibs() to resolve
  library names using the introspection binary.
tests/scanner/Makefile.am: Add .libs to LD_LIBRARY_PATH

http://bugzilla.gnome.org/show_bug.cgi?id=591669