Add YouCompleteMe support

YouCompleteMe[1] is a vim plugin that implements semantic
code completion using libclang.

For non-trivial projects such as libvirt, the plugin needs
some help figuring out where to find the various header
files: generate its configuration file at configure time
so that the plugin works out of the box.

[1] http://valloric.github.io/YouCompleteMe/

.gitignore

@@ -36,6 +36,7 @@
 .lvimrc
 .memdump
 .sc-start-sc_*
+.ycm_extra_conf.py
 /ABOUT-NLS
 /AUTHORS
 /ChangeLog