DOC: exclude directories .git for doxygen documentation

Documentation/Doxyfile.txt.in

@@ -674,7 +674,8 @@ EXCLUDE_SYMLINKS       = NO
 # for example use the pattern */test/*
 
 EXCLUDE_PATTERNS       = moc_*.cxx \
-                         ui_*.h
+                         ui_*.h \
+                         */.git/*
 
 # The EXCLUDE_SYMBOLS tag can be used to specify one or more symbol names
 # (namespaces, classes, functions, etc.) that should be excluded from the