Add font path for Mac OS X.
Skip build in case the library is already installed.
Patch Qt when building on Mavericks/XCode 5.0.1.

This is a workaround for compilation problems in that
environment:

- Disable tiff plugin which fails with duplicate symbol
  errors when linking. This is available as configure option.

- Disable core-wlan which fails compilation with lots
  of errors. This needs to patch the qmake config file.