[hgbook] Fix a typo

[Dongsheng Song]

diff -r 96ea24a916f9 en/cmdref.tex
--- a/en/cmdref.tex     Mon Nov 26 20:42:36 2007 -0800
+++ b/en/cmdref.tex     Sat Dec 08 09:01:09 2007 +0800
@@ -29,11 +29,11 @@ that contains only whitespace is not con

 \optref{diff}{I}{include}

-Exclude files and directories whose names match the given patterns.
+Include files and directories whose names match the given patterns.

 \optref{diff}{X}{exclude}

-Include files and directories whose names match the given patterns.
+Exclude files and directories whose names match the given patterns.

 \optref{diff}{a}{text}

Dongsheng Song