[Doxygen-develop] make clean and make distclean in src

[Maik H. <ma...@hi...>]

Hello,

I would like to suggest following small changes in src/Makefile.in:

1. "make clean" should remove generated source files by lex and bison, so I 
moved files from distclean to clean.

2. "make distclean" should remove file lang_cfg.h (generated by configure).

Please find attached diff file.

Cu,
Maik