Tell Git to export '.gitattributes'

Since we do not package the KWSys source tree directly and always
merge snapshots of its content into other project subtrees, we
should carry the .gitattributes file into the other projects to
that the attributes apply in their source trees too.

Change-Id: I039b151443486d24ff798fa0c677b62620cec0b7

.gitattributes

 .git*            export-ignore
+.gitattributes  -export-ignore
 
 /GitSetup        export-ignore
 /SetupForDevelopment.sh  export-ignore  eol=lf