Fix running VisualStudio env when building

[spsalefeve]

This PR fixes Issue #974 .

[nerdvegas]

I can't merge this PR yet, but it's on the right track. You are right in that CMAKE_MODULE_PATH should be getting set earlier, I think.

I think the reason post_actions_callback was being used is because this is where pre_build_commands is getting run from. With this PR, pre_build_commands would get run before package commands, instead of after, and I can see that breaking existing behaviour for some users (it also feels correct that pre_build_commands should be run as late as possible, but before the build - this is intuitive).

I think what we need to do is:

• split BuildSystem.add_standard_build_actions so that pre_build_commands setup is done in another method (eg add_pre_build_commands)
• keep the change in this PR that uses actions_callback instead, but also add a post_actions_callback that calls add_pre_build_commands.

In other words, we want what this PR is doing, but pre_build_commands should always be run via post_actions_callback instead.

Please note that this change needs to be done in all the build system plugins, not just cmake, for reasons of consistency. Fortunately it looks like a pretty trivial change.

Thx
A