After a build finishes, if it returned file comments, the executor
will use the repo in the workspace (if it exists) to map the
supplied line numbers to the original lines in the change (in case
an intervening change has altered the files).
A new facility for reporting warning messages is added, and if the
executor is unable to perform the mapping, or the file comment syntax
is incorrect, a warning is reported.
Change-Id: Iad48168d41df034f575b66976744dbe94ec289bc
James E. Blair
4e70bebafb