lh#cpp#file#HeaderName shall be able to return a path relative to a specific directory and not to the current path.

[GoogleCodeExporter]

What steps will reproduce the problem?
1. mu-template 2.0.3 + patched a.vim from lh-cpp
2. The following files: root/inc/foo.h, root/src/cpp/foo.cpp, 
3. Have a local vimrc in root that sets:
{{{
let b:sources_root = expand('<sfile>:p:h')
let g:alternateSearchPath = 'reg:#/src/cpp#/inc#,reg:#/inc#/src/cpp#'
}}}
4. edit root/src/cpp/foo.cpp
5. change directory to root/src/cpp/
6. `:echo lh#cpp#file#HeaderName(expand('%:p'))`

What is the expected output? 
`root/inc/foo.h`

What do you see instead?
`/absolute/path/to/root/inc/foo.h`

_Conclusion_
The path returned shall be made relative to `b:sources_root`. May be it
shall be an option that mu-template could take advantage of.
The error actually appears when first creating, from within vim, foo.cpp
from src/cpp/.

Original issue reported on code.google.com by luc.herm...@gmail.com on 20 May 2010 at 10:59