convert: tolerate spaces between splicemap parent ids (issue3203)

Splicemap lines are documented in hg help convert like:

  key parent1, parent2

but parsed like:

  key, parents = line.strip().rsplit(' ', 1)
  parents = parents.replace(',', ' ').split()

The rsplit() call was introduced to handle spaces in keys for the generic
mapfile format. Spaces can appear in svn identifiers since they contain path
components. This logic makes less sense with splicemap since svn identifiers
can also appear on the right side, even if it is a bit less likely. Given the
parsing is theorically broken, I would rather follow what is documented already
and is correct in the main case where all identifiers are hg hashes. Also,
using svn identifiers in a splicemap sounds difficult as they are not easily
accessible.

hgext/convert/common.py

@@ -419,7 +419,7 b' def parsesplicemap(path):'
         fp = open(path, 'r')
         for i, line in enumerate(fp):
             try:
-                child, parents = line.splitlines()[0].rstrip().rsplit(' ', 1)
+                child, parents = line.splitlines()[0].rstrip().split(' ', 1)
                 parents = parents.replace(',', ' ').split()
             except ValueError:
                 raise util.Abort(_('syntax error in %s(%d): child parent1'