FindQCA2.cmake changes

[Michel Hermier]

Michel Hermier wrote:
> Hi,
> Here are my changes to make FindQCA2.cmake working for me (the path 
> were broken for me).
> I changed it so it follows what other find scripts do:
> - using the cache (don't know if it's rigth to do so)
> - Check the presence of the libraries for dynamic compilation instead 
> of relying on pkg-config only (maybe this also fix things on WIN32, I 
> don't really know)
>
> Comments or OK to commit ?

2 days without comment or objections. Commiting as this (#609041).
Report QCA2 search breakage to me so that I can take proper actions.

Michel