[gfortran] add ISATTY and TTYNAM intrinsics

[FX Coudert]

Attached patch (with testcase and ChangeLog entries) adds g77 ISATTY and 
TTYNAM intrinsics to gfortran.

Built and regtested on i686-linux. OK for mainline and 4.0?

FX
:ADDPATCH fortran:
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