libyaml: updated to 0.2.5

0.2.5:
Allow question marks in plain scalars in flow collections
Emitter: Don't output trailing space for empty scalar nodes
Emitter: Output space after an alias mapping key
Add -h and --flow (on|off|keep) to run-*-test-suite
Remove unnecessary include and malloc
Add specific files back to .gitignore
Output error position in run-parser-test-suite.c
A couple patches to improve test suite support

(adam)