safehasattr: pass attribute name as string instead of bytes
This is a step toward replacing `util.safehasattr` usage with plain `hasattr`.
The builtin function behave poorly in Python2 but this was fixed in Python3.
These change are done one by one as they tend to have a small odd to trigger
puzzling breackage.
https://bz.mercurial-scm.org/1089
$ hg init repo
$ cd repo
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..