* m4/log2-ieee.m4: New file.
* m4/log2.m4 (gl_FUNC_LOG2): If gl_FUNC_LOG2_IEEE is present, test
whether log2 works with a minus zero argument. Replace it if not.
* modules/log2-ieee (Files): Add m4/log2-ieee.m4.
(configure.ac): Invoke gl_FUNC_LOG2_IEEE.
* doc/posix-functions/log2.texi: Mention the log2-ieee module.
* lib/math.in.h (log2): New declaration.
* lib/log2.c: New file.
* m4/log2.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether log2 is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_LOG2, HAVE_DECL_LOG2,
REPLACE_LOG2.
* modules/math (Makefile.am): Substitute GNULIB_LOG2, HAVE_DECL_LOG2,
REPLACE_LOG2.
* modules/log2: New file.
* tests/test-math-c++.cc: Check the declaration of log2.
* doc/posix-functions/log2.texi: Mention the new module and the IRIX
and OSF/1 and Cygwin problems.
* m4/printf.m4 (gl_PRINTF_INFINITE_LONG_DOUBLE): Don't guess yes on
MacOS X; the test fails on MacOS X 10.5.8.
* doc/{glibc,posix,pastposix}-{headers,functions}/*.texi: Update info
about MacOS X.
