Fix constructor to match parent class
Changes to cs_lockfile for consistency + testability

 * constructor requires path as 1st argument
 * lockfile name is optional 2nd arg, defaults to "upgrade.lock"
 * uses InvalidArgumentException unless path is directory with +rw
 * get_rwdir() is simpler: ensures this->rwDir is a directory then returns it
 * get_lockfile() returns full path to lockfile
 * set_lockfile() doesn't bail when passed name & new name are the same
 * is_lockfile_present() concatenates rwDir + lockfile instead of calling get_lockfile()
Changes to cs_sessionDB for testing

 * use "self::$runDate" instead of "cs_sessionDB::$runDate" to avoid issues if class name changes
 * is_valid_sid() doesn't bail when passed $sid is < 20 characters long: this caused tests to fail, even when they shouldn't have
 * better error checking on doInsert
 * sessdb_gc() overhauled to be simpler/straightforward (still needs work)
 * exception_handler() tests for cs_backtrace() before calling it
 * ignore flogger() for test coverage
Changes to cs_webdbupgrade for testability + stability

 * allow passing of "rwDir" to constructor
 * is_lockfile_present() sets RWDIR before creating a new cs_lockfile
 * don't create/reset cs_lockfile object in reconnect_db()
 * remove unnecessary/redundant create_lockfile() method
Updates to match changes in code
Updated documentation