Tell Git to not export 'clang-format' infrastructure

These files are only for development of KWSys itself and are not
needed when the source tree is merged into clients.

Change-Id: Ie4a42cae5bcf8993df958af178d3c5359684c598

.gitattributes

@@ -3,6 +3,8 @@
 
 /GitSetup        export-ignore
 /SetupForDevelopment.sh  export-ignore  eol=lf
+/clang-format.bash export-ignore eol=lf
+/.clang-format   export-ignore
 
 /CONTRIBUTING.rst conflict-marker-size=78