Fix wrong example in fftw-wisdom-to-conf.1

Thanks Julian Taylor for the bug report.
Fix autodetection of cosl(), sinl()

Autoconf must have changed since we last looked.  Thanks
Åke Sandgren for the fix.
Be more careful in detecting sinl(), cos(), memalign(), posix_memalign()
group together AC_CHECK_DECLS for functions in stdlib.h
document fftw_alignment_of (since I found it useful in Julia, other people may too)
added fftw_sprint_plan to output plan info to a string (so that the caller can be more flexible about how it is displayed)
Merge pull request #1 from FFTW/master

update from FFTW/fftw3