rebase: improve error message for --base being empty or causing emptiness
Before it just said 'nothing to rebase'.
Now 'if "base" is an empty set:
abort: empty "base" revision set - can't compute rebase set
If the set of changesets to rebase can't be found from "base", it will fail as
before but with more explanation of what the problem was.
The name of the "base" option is not obvious - it is more like "samples
identifying the branch to rebase". The error messages for problems with the
specified "base" value will use that term and might thus also not be obvious,
but at least they are consistent with the option name. The name "base" will not
be used if the base only was specified implicitly as the working directory
parent.
#if unix-permissions no-root
$ hg init a
$ echo a > a/a
$ hg -R a ci -A -m a
adding a
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo b > b/b
$ hg -R b ci -A -m b
adding b
$ chmod 100 a/.hg/store
$ hg -R b push a
pushing to a
abort: could not lock repository a: Permission denied
[255]
$ chmod 700 a/.hg/store
#endif