boot.js passes the absolute path to the loaded source

relative paths confuse node-inspector and possibly other tools
Reference source-map in the server-side code's source

It is not needed for mapped stack-traces but is necessary for node-inspector.
Use the filepath from builder in the sourceMappingURL ref
Prefer += operator for strings concatenation to String#concat
Resolve paths with path.resolve
For files with source maps, use absolute paths map the stack-trace. If no source
map found, don't bother.
Update the comment
Merge branch 'server-source-maps' into devel

Enables the support for source maps for the server-side code.
It is very useful when toolings like node-inspector or node-profiler are used.