(CFACT-158) Use rb_block_call instead of rb_funcall_with_block.

rb_funcall_with_block was added in a later 1.9.3 patch.  To support all
1.9.3 versions, use rb_block_call instead.

rb_block_call provides the exact same functionality we need, but doesn't
require us to wrap the C func in a Ruby proc.
(maint) Fix Clang issue with ignored GCC warning

GCC introduced a maybe-uninitialized warning that Clang doesn't
recognize, but Clang does try to interpret all GCC diagnostic pragmas.
Move the warning to be ignored in CMake; it's relatively new and likely
to cause problems with 3rd-party libraries.
Merge pull request #221 from peterhuene/cfact/158

(CFACT-158) Use rb_block_call instead of rb_funcall_with_block.
(CFACT-159) Add support to build trusty packages
Merge pull request #223 from melissaanne/master

(CFACT-159) Add support to build trusty packages
Merge pull request #222 from MikaelSmith/maint/master/fix-clang-missing-warning

(maint) Fix Clang issue with ignored GCC warning