tests/test-rebase-abort.out

tests: fix bashism to load helpers.sh

`source` isn't available at POSIX sh.

1 files updated, 0 files merged, 0 files removed, 0 files unresolved
created new head
@  4: L2
|
o  3: L1
|
| o  2: C3
|/
o  1: C2
|
o  0: C1


% Conflicting rebase
warning: conflicts during merge.
merging common failed!
abort: fix unresolved conflicts with hg resolve then run hg rebase --continue
merging common

% Abort
saved backup bundle to 
rebase aborted
@  4: L2
|
o  3: L1
|
| o  2: C3
|/
o  1: C2
|
o  0: C1