Adds sigtermTime to RemoteShellCommand

Adds the parameter sigtermTime to RemoteShellCommand. If sigtermTime is
not None, the buildslave will fire SIGTERM and wait for sigtermTime
seconds before firing SIGKILL. This fixes trac ticket #751.
Adds test_sigterm and updates tests to reflect new parameter
Documentation updates for sigtermTime
Adds sigtermTime default to fake runprocess
remove redundant 'return' statement
enable E0101 (return-in-init) pylint check
Waiting for sigterm is now nonblocking
Check slave version before supplying sigtermTime param
Updates relnotes
Patch for ticket 2560.
Fixes version checking
Modified tests.
fixed typo
check --db parameter for 'buildbot create-master' command

Check that database URL specified via --db parameter is valid. Print
usage error otherwise.
Increment version and update relnotes
Merge branch '751-fire-sigterm-before-sigkill' of git://github.com/markberger/buildbot
Merge branch 'ticket_2560' of git://github.com/ewongbb/buildbot
Merge branch 'pylint-return-in-init' of git://github.com/elmirjagudin/buildbot
fix and enable empty-docstring (C0112) pylint check
buildstep.py: Add support for description{,Done}

Add support for attributes description and descriptionDone in the
BuildStep class. This means that any subclass of BuildStep will also
support these attributes as well. This was not previously the case.