doxygen: allow building on 10.7.

Adds an inreplace command modifying "qtools/qglobal.h" to allow building on Mac
OS X 10.7. Previously, there was an OS version check resulting in a preprocessor
error directive.  This changes the error to a warning, allowing compilation to
continue. A patch has been submitted to doxygen to fix this properly (i.e. in
the source), and should be in the next version, so this change can be safely
removed when the next version arrives.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Formula/doxygen.rb

@@ -12,6 +12,14 @@ def install
       # Path of man1 relative to already given prefix
       s.change_make_var! 'MAN1DIR', 'share/man/man1'
     end
+
+    # This allows compilation against 10.7 Lion, by changing a preprocessor
+    # OS version check error to a warning. A bug report has been filed
+    # upstream (https://bugzilla.gnome.org/show_bug.cgi?id=650463). This
+    # should be fixed in the next version of Doxygen, so the following line
+    # can and should be removed when it is released.
+    inreplace "qtools/qglobal.h", "    error", "    warning"
+
     system "make"
     system "make install"
   end