.git*: add gitattributes and gitignore

For users of the git mirrors, lets provide useful git configuration
files.

.gitattributes

@@ -0,0 +1,5 @@
+*.c    diff=cpp
+*.h    diff=cpp
+*.cpp  diff=cpp
+*.hpp  diff=cpp
+*.py   diff=python

.gitignore

@@ -0,0 +1,18 @@
+_.tinderbox.*
+_.amd64.*
+_.arm.*
+_.arm64.*
+_.i386.*
+_.ia64.*
+_.mips.*
+_.pc98.*
+_.powerpc.*
+_.riscv.*
+_.sparc64.*
+_.sun4v.*
+GPATH
+GRTAGS
+GTAGS
+ID
+cscope.out
+?cscope.out