filemerge: only copy to backup during premerge step The premerge might leave the original file in an unclean state. Therefore it's important to only copy the file in the beginning.

filemerge: only print out "merging f" output at premerge step We're soon going to call this function twice, once for premerge and once for merge. This makes sure the "merging" output only gets printed during the premerge step.

filemerge: deindent the parts of filemerge outside the try block It is no longer necessary to indent these parts.

filemerge: introduce a premerge flag and function This flag will let us get to our overall goal of performing all premerges before any merges.

filemerge: also return whether the merge is complete In future patches, we'll pause merges after the premerge step. After the premerge step we'll return complete = False.

filemerge: add a wrapper around the filemerge function We'll introduce a separate premerge function that calls the same code.

context: don't hex encode all unknown 20 char revision specs (issue4890) d3908c911d5e introduced nice hexified display of missing nodes. It did however also make missing 20 character revision specifications be shown as hex - very confusing. Users are often wrong and somehow specify revisions that don't exist. Nodes will however rarely be missing ... and they will only look like a user provided revision specification and be all ascii in 1 of 4*10**9. With this change, missing revisions will only be hexified if they really look like binary nodes. This change will thus improve the error reporting UI in the common case and only very rarely make it confusing in the opposite direction of how it was before.

discovery: put trivial branch first Having the simple and tiny branch of the conditional first help readability. The "else" that appears after a screen of code is harder to relate to a conditional.