make install

[Michael Becker <mb12@coconet.de>]

  minor makefile typos:

install-dirs:
        -mkdir $(prefix)
        -mkdir $(execfix)   # should be exec_prefix

  something like 
       
install-dirs:
        - [ -d "$(prefix)" ]      || mkdir $(prefix)
        - [ -d "$(exec_prefix)" ] || mkdir $(exec_prefix)
       ....


  would be better, because '/usr/local' , '/usr/local/bin'  etc will  exists


 - michael