Comply with R's error reporting conventions.

R usually reports errors with a full path on a separate line. Something like

    Error in source(file = "c:/spinus/works/pbm/protoClasses.R") :
    c:/spinus/works/pbm/protoClasses.R:374:31: unexpected ', '
    373:                                  .initCells(dots,  .self)

It is good to comply with this convention, as some IDEs (for example ESS) can
track this errors and navigate directly to the error location.
Merge remote-tracking branch 'vitoshka/master' into develop