Add a .gitignore file

This makes it easier to setup new git repositories, and makes it more
likely all people have the same ignore rules.

Reviewed-by: imsnah

.gitignore

+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~
+
+# global ignores
+*.py[co]
+
+# /
+/Makefile
+/Makefile.in
+/TAGS
+/aclocal.m4
+/autom4te.cache
+/autotools
+/config.log
+/config.status
+/configure
+/ganeti
+/*.patch
+/*.tar.bz2
+/*.tar.gz
+
+# devel
+/devel/clean-cluster
+/devel/upload
+
+# doc
+/doc/*.html
+/doc/*.in
+/doc/*.pdf
+
+# doc/examples
+/doc/examples/ganeti.cron
+/doc/examples/ganeti.initd
+
+# lib
+/lib/_autoconf.py
+
+# man
+/man/*.[0-9]
+/man/*.in