p4_dscm. Remove error on empty path from p4 depot path to local

The path can be empty (not a file) if the p4 file was removed or added in
the syne.
p4_dscm. Complete implementation of change command.
p4_dscm. Bug fixes.

Only close the log file, if the log option was used.
Fix an issue in p4 path to local path, put the path inside "" so that p4
will handle spaces correctly in the path.
Fix an issue in get change list description, add '-' to the regular
expression match for the files in the change list.