Is there any way I can enter a particular filename - e.g. "xyz.txt" - and search for any checkins of that file within a Mercurial repository using TortoiseHG?
If not, why not? Isn't this what version control is for?
In the "Hg Repository Explorer" window choose the "File Patterns" filter in the combo box and type the name of the file (e.g., xyz.txt) in the field next to it and hit return. You would now see only the revisions where xyz.txt was modified. If you want to search your entire directory structure (rather than just the folder you are currently in) then add "**" (e.g. **xyz.txt).