Release 2.1.8

This is primarily a maintenance release to assure that build problems
on some distros are addressed in released code, but there are a few bug
fixes in it as well.

• The Xastir project no longer provides tar files that have been
  "bootstrapped" --- all users of Xastir source must now run
  "bootstrap.sh" to create the configure script irrespective of how
  they've obtained the code (through a release tarball, github
  master branch tarball or git clone).

• If Xastir crashes, instances of the network server no longer stick
  around to interfere with starting up a new copy of Xastir. (issue
  #130)

• The get-NWSdata script now correctly respects the install prefix in
  all its steps (pull request #172)

• Xastir's probe for libproj no longer looks for the deprecated
  function pj_init, making it compatible with newer versions of the
  proj library. (issue #173)

• Some unused, buggy diagnostic code has been removed. This code was
  causing segfaults on some systems. (issue #174)

• Some debugging code that was unintentionally left in place caused
  Xastir to output some diagnostic information to standard error,
  leading users to think there was a problem. The information was
  unimportant to anyone but a developer working on that bit of the
  code, and was not indicative of a problem at all. It has been
  removed.

• Some very ancient autoconf code was updated to work with more
  recent versions of autoconf. This removes several deprecation
  warnings, but more importantly removes fatal errors in the most
  recent version of automake (pull request #181)

• The "install-xastir" script has been removed. Users are encouraged
  to read the INSTALL document follow all directions. There is no
  shortcut, and the presence of this script implied that there was.