Fix RunCMake.no_install_prefix test on VS 6

Pass the CMAKE_INSTALL_PREFIX cache entry with a type.  The cache
entry argument parsing compiled by VS 6 seems buggy without the
type, which will have to be tracked down separately from this topic.
Merge topic 'add-CMAKE_FIND_NO_INSTALL_PREFIX' into next

4ac5dd3 Fix RunCMake.no_install_prefix test on VS 6
Allow disabling adding the install prefix to the prefix search path.

In certain scenarios, it is preferable to keep a 'dirty' install prefix
than to clear it, and to expect that content will not be found there.
Add a CMAKE_FIND_NO_INSTALL_PREFIX variable that can be set to
searching the install prefix.
Merge topic 'add-CMAKE_FIND_NO_INSTALL_PREFIX' into next

d184a9f Allow disabling adding the install prefix to the prefix search path.