Rolling code for version 2.21

Debian release 2.20

Changelog update before release.

Issue #103: Child process cleanup under PAM session

* Added signal handling in PAM session process. Now SIGHUP signals are
  forward to child process, which is the actual service. Launcher process
  uses this type of signals to terminate service on http connection
  timeout.

Package release commit.

Release to guarantee upgrade.

Debian release.

Fixes for some defects found by Coverity

* Added more checks for return values and null pointers.
* Removed some dead code and unused variables.
* Fixed handling of calls to exec() family functions. If this functions
  fail we need to cleanup resources.

Fixing errors reported by piuparts.

o Revised debian/rules dh_install.
o Revised postrm and prerm.

Debian release 2.13-1.