cmake: Correct typo's in CMake output config file
cmake: Add pkgconfig DIR to output config file

This indicates where the .pc pkgconfig files are installed, which
more easily allows dependent packages to use typegen with KDL like:

SET(PKG_CONFIG_PATH "${orocos_kdl_PKGCONFIG_DIR}")
orocos_typegen_headers(xxx.hpp DEPENDS orocos_kdl)
Merge pull request #18 from snrkiwi/cmake-fixes

CMake config file fixes