Merge branch 'rs/help-c-source-with-gitattributes'

The .c/.h sources are marked as such in our .gitattributes file so
that "git diff -W" and friends would work better.

* rs/help-c-source-with-gitattributes:
  .gitattributes: set file type for C files

.gitattributes

@@ -1,3 +1,3 @@
 * whitespace=!indent,trail,space
-*.[ch] whitespace=indent,trail,space
+*.[ch] whitespace=indent,trail,space diff=cpp
 *.sh whitespace=indent,trail,space