obsolete: flip `obstore.successors` and `obsolete.precursors`
People were confused by the fact `obstore.precursors` contained marker allowing
to find "precursors" and vice-versa.
This changeset changes their meaning to:
- precursors[x] -> set(markers on precursors edges of x)
- successors[x] -> set(markers on successors edges of x)
Some documentation is added to clarify the situation.
$ hg init
$ echo 0 > a
$ echo 0 > b
$ hg ci -A -m m
adding a
adding b
$ hg rm a
$ hg cat a
0
$ hg cat --decode a # more tests in test-encode
0
$ echo 1 > b
$ hg ci -m m
$ echo 2 > b
$ hg cat -r 0 a
0
$ hg cat -r 0 b
0
$ hg cat -r 1 a
a: no such file in rev 7040230c159c
[1]
$ hg cat -r 1 b
1
Test fileset
$ echo 3 > c
$ hg ci -Am addmore c
$ hg cat 'set:not(b) or a'
3
$ hg cat 'set:c or b'
1
3