Clean webvtt-config.h.

According to the examples in the automake manual, BUILD_SOURCES
resolves the dependency generation race, but doesn't actualy add
the built sources to the clean file list. We need to do this
explicitly to make sure it's removed from the tree on 'clean'.

This commit has 'make distcheck' working for me for the first time.
Make webvtt-config.h depend on Makefile.

This way it gets remade if the generating rule might have changed.
Modified .travis.yml to test 'make distcheck' as well. In addition, also trying to send irc notifications to #seneca on irc.freenode.net now.
Updated test/unit/Makefile.am to list subdirectories containing test files in EXTRA_DIST
Append to EXTRA_DIST instead of clobbering it.

The gtest fragment EXTRA_DIST line was shadowing the earlier
one for the test file subdirectories. Bad merge.
Mark failing tests as XFAILs instead of disabling them.

GTest has a mechanism for marking tests as disabled when
they're not ready. Automake has another method, where executables
can be marked as 'expected to fail'.

The gtest method has finer granularity, but the automake
method is more transparent about what's working and what's
not.

This commit enables everything but
CueIdLanguage.DISABLED_LongStringMultipleLanguages which hangs in
an inifinite loop. All of the unit tests are added to the XFAIL
list since none of them completely pass at this point.
Merge branch 'xfail-tests' of git://github.com/rillian/webvtt into bug-test
Fixed bug that was introduced in last bug fix where some parsing functions needed to retain the new line from webvtt_string_getline while others did not. Added in an option to specify whether or not you'd like the new line returned with the string in webvtt_string_getline.