Include strings.h for strcasecmp()
configure.in should be called configure.ac to work with latest autoconf.

Fixed so compiles with "./configure --enable-paranoia" with gcc 4.2.1 on
FreeBSD 9.1:

  * Define _XOPEN_SOURCE == 600 for (at least) lrand48()
  * Replaced obsolescent bcopy() with memmove()

_XOPEN_SOURCE == 700 isn't possible yet due to the use of several
obsolescent interfaces.

Include "strings.h" for strcasecmp() where I neglected to do this.