(size_input_section): maintain the delta information.
* ldlang.h: add new field to struct to contain delta info.
* relax.c (relax_section): complain if input not relaxable.
* ldlex.l : add '_', ',' and '$' to chars which can appear at the
start of a filename
to be "-".
* ldsym.c, ldlang.c: remember that size of a section is dependent on
whether or not relaxing has been done.
* ldmain.c: don't open a map file if it doesn't have a name
* relax.c: all the brains have moved into bfd.
* ldwrite.c: ammend comment
