[MacPorts] #44193: qt: allow side by side installation of qt4-mac and qt5-mac

[David Evans]

On 6/30/14 1:26 PM, MacPorts wrote:
>  (2) I would say that using a private prefix for Qt 5 is "good enough" for
>  now unless the software would link against Qt 4 by accident (just because
>  `-I${prefix}/include` contains Qt 4 for example).
This is definitely a possibility.  A current example is lua5.1 vs lua. 
Lua is installed
in ${prefix} and lua5.1 in a subdirectory.  Unless the port that needs
lua5.1 is configured to include
the subdirectory first (not the default), the port will pickup lua
instead and misconfigure.  Boswars
is an example port where this occurred.

I strongly urge putting each of the versions in their own subfolders,
even if this requires re-configuring existing ports.  This
way neither will override the other by default, its the maintainers
choice as to which version is used and the necessary configuration
options will be somewhat symmetrical between the two versions.

By the way poppler has bindings for both qt4 and qt5 and they are not
the same at all so there is at least one instance of
difference in existing ports.  My intention is to add a qt5 subport
similar to the current qt4 one as soon as this issue of
parallelism is resolved.

Dave