EA-43592 - NPE: Alarm$Request.toString
[vcs] rename method to match it function
[diff] IDEA-100386 Detect file type for temporary files built for diff

Otherwise non-binary files without file type associated with them are treated as binary, because file type is not detected for this manually constructed temporary VirtualFiles.
Refactor error title if mercurial log command failed.

*Add notification title to HgVcsMessages.
IDEA-99083 Conflict Resolver displays wrong base version when using Mercurial / hg

*Get common ancestor for 2 revisions using hg log command.