feat(third_party/lisp/s-xml): Check in sources & derivation

Checked in the sources for this because it is tracked upstream in CVS
and I can't be bothered to deal with that right now.

third_party/lisp/s-xml/.gitignore

@@ -0,0 +1,28 @@
+# CVS default ignores begin
+tags
+TAGS
+.make.state
+.nse_depinfo
+*~
+#*
+.#*
+,*
+_$*
+*$
+*.old
+*.bak
+*.BAK
+*.orig
+*.rej
+.del-*
+*.a
+*.olb
+*.o
+*.obj
+*.so
+*.exe
+*.Z
+*.elc
+*.ln
+core
+# CVS default ignores end