tests/histedit-helpers.sh

tests: restore 'python' and '$TESTDIR/' for dummyssh invocation

This is a backout of 46727fea7a00, and a partial backout of c3ecbf694904.

Windows won't execute 'dummyssh' directly, presumably because CreateProcess()
doesn't know how to execute a bash script:

   $ hg clone -e "dummyssh" ssh://user@dummy/cloned sshclone
   remote: 'dummyssh' is not recognized as an internal or external command,
   remote: operable program or batch file.
   abort: no suitable response from remote hg!
   [255]

With the restoration of python as the executable, $TESTDIR needs to be restored
for these invocations, because python won't search $PATH for 'dummyssh':

   $ hg clone -e "python dummyssh" ssh://user@dummy/cloned sshclone
   remote: python: can't open file 'dummyssh': [Errno 2] No such file or directory
   abort: no suitable response from remote hg!
   [255]

fixbundle() {
    grep -v 'saving bundle' | grep -v 'saved backup' | \
        grep -v added | grep -v adding | \
        grep -v "unable to find 'e' for patching" | \
        grep -v "e: No such file or directory"
}