Add an "Adventure II" Makefile; allow compiling with gfortran.

As I'm using OSX as my primary development environment these days, and
fort77/f77 don't seem to have made it to Homebrew yet, it's suddenly
useful to me to be able to compile these Fortran programs with GNU
gfortran. I've edited all three "original Fortran" Makefiles to run
"which f77; which gfortran" and pick the most f77-like option (or fail
if you have no Fortran compiler on your system).

On Ubuntu Linux, you'll want to run
    sudo apt-get install fort77
On OSX, the appropriate command is
    brew install gfortran

Unfortunately, GNU gfortran isn't as faithful to these old dialects as
the f77 compiler was...

  - In LUPI0440/, I needed to add "EXTERNAL RAN" in two places to prevent
gfortran from mistakenly using its built-in RAN function instead of the
one defined in the program itself.

  - In PLAT0550/, I needed to replace the syntax "INTEGER x*4" with
"INTEGER*4 x", since gfortran doesn't accept the former syntax at all.

However, these changes are small enough, and provide enough of a benefit
(Adventure II is now playable on OSX!) that I'm sure they're worthwhile.