Changes made to the extlib files:

- General:
  * Append _simput to heasoft libraries to avoid confusion during linking.
  * All changes in the source code are commented with "SIMPUT".

- cfitsio:
  * rename library name from cfitsio to cfitsio_simput

- wcslib:
  * set version to 7.7_simput
  * when updating the wcslib, LIBVER in extlib/Makefile.am (L60) must
    also be updated accordingly

- fftw:
  * rename library name from fftw3 to fftw3_simput
  * commented out "AC_DISABLE_SHARED" in configure.ac, L33.
  * fftw/doc directory not compiled for Simput, commented out corresponding lines
    in Makefile.am L34-42 and deleted corresponding AC_CONFIG_FILES entries in
    fftw/configure.ac, L805-806 (creating the documentation also modifies many
    of the input files there which leads to problems with git and also
    'make distcheck').

- ape:
  * src/ape_io.c (L1432-1439): Added message about deprecated Mission,
    Instrument, and Mode parameters if they are still used when executing a
    Sixte tool (this XML selection feature was removed with Sixte commit e5e30e89).
