Post-release version bump to 1.12
build-sys: Fix parallel build

On my machine, parallel builds fail with:

make[2]: Entering directory `/home/teuf/hack/libplist/src'
  CCLD     libplist.la
make[2]: *** No rule to make target `../src/libplist.la', needed by
`libplist++.la'.  Stop.

If $(top_builddir)/src/libplist.la does not exist yet when trying to
link libplist++.la, automake/make will not realize the
$(top_builddir)/src/libplist.la dependency is the same as the
libplist.la target, and will thus be unable to generate
$(top_builddir)/src/libplist.la.

Using the libplist.la instead fixes this issue.

I've checked that srcdir!=builddir and make distcheck still pass after
this change.
Fix endian detection in configure.ac

On debian-mips, neither __LITTLE_ENDIAN__ nor __BIG_ENDIAN__ are defined
anywhere, so PLIST_BYTE_ORDER defaults to PLIST_LITTLE_ENDIAN when it should
really be PLIST_BIG_ENDIAN on this architecture.

This fixes issue #13.
Drop manual endian.h header check

AC_C_BIGENDIAN should do its job already.
xplist: Fix timezone-bound date/time conversion
test: Add new timezone tests
Simplify plist_dict_merge() after plist_dict_set_item() API change
test: Fix timezone test cases with set -e
Merge branch 'master' of https://github.com/libimobiledevice/libplist