Allow stage/install rule to copy files to folders relative to the Boost Build build folder.

[jurko .gospodnetic@…]

Boost Build should allow installing targets (using the install/stage rule) to paths relative to the regular Boost Build build path instead of only relative to the target folder where the project's Jamfile is located.

Example:

If 'exe aaa : aaa.cpp ;' builds the aaa.exe file in the bin/msvc-7.1/debug/threading-multi folder then we would like to copy an additional aaa.txt file to that same location.

It is possible to achieve this effect partially already by using the following poor-man's solution:

import make ; make aaa-copy.txt : aaa.txt : @common.copy ;

However there are a several things 'wrong' with this solution:

1. It is not exactly the most intuitive line of code for what you want it to do.
2. Forces you to duplicate file name information.
3. There is no way to make the file keep its original name.
4. Does not work with multiple source files.
5. Does not have any extra install rule logic like install-source-path feature or shared library relinking support.