main/xulrunner: upgrade to 5.0.

all patches have been rebased as needed, with the following exceptions:

gecko-c99math.patch: dropped.

xpcom-c99math.patch: new patch, replacing the NS_finite() call which was added to
                     xulrunner, at some point after xulrunner-2.0 was released.
                     in all reality, this replaces the old gecko-c99math patch.

mozilla-bsdiff-libbz2.patch: new patch, fixes build when using system libbz2.  patch care
                             of Mike Hommey <glandium@debian.org>, see mozilla bug number
                             644692.  hopefully, this will make it into xulrunner-6.0.

mozconfig: add --disable-elf-hack because of incompatibility with preload and current alpine
           psABI.