[gfortran,patch] Add ISNAN intrinsic

[FX Coudert]

This patch adds an ISNAN intrinsic as a GNU extension, since others  
compilers have it (ifort, g95, sunf95, sgi) and some code relies on  
it (http://www.libatoms.org/). The patch is simple, comes with a  
testcase and documentation written by Tobias Burnus (slightly  
modified by me).

Regtested on x86_64-linux, OK to commit?
FX


:ADDPATCH fortran:
-------------- next part --------------
A non-text attachment was scrubbed...
Name: isnan.ChangeLog
Type: application/octet-stream
Size: 618 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/fortran/attachments/20070804/e0f44783/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: isnan.diff
Type: application/octet-stream
Size: 5375 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/fortran/attachments/20070804/e0f44783/attachment-0001.obj>