changegroup: rename _computeoutgoing to computeoutgoing

changegroup: rename _computeoutgoing to computeoutgoing

We're going to use this function from another module in an upcoming
patch. Drop the _ prefix to mark it as non-private.

--- a/mercurial/changegroup.py	Tue Jun 02 13:24:39 2015 -0500
+++ b/mercurial/changegroup.py	Tue Jun 02 19:58:06 2015 -0700
@@ -615,7 +615,7 @@
     bundler = cg1packer(repo, bundlecaps)
     return getsubset(repo, outgoing, bundler, source)
 
-def _computeoutgoing(repo, heads, common):
+def computeoutgoing(repo, heads, common):
     """Computes which revs are outgoing given a set of common
     and a set of heads.
 
@@ -646,7 +646,7 @@
     The nodes in common might not all be known locally due to the way the
     current discovery protocol works. Returns a raw changegroup generator.
     """
-    outgoing = _computeoutgoing(repo, heads, common)
+    outgoing = computeoutgoing(repo, heads, common)
     return getlocalchangegroupraw(repo, source, outgoing, bundlecaps=bundlecaps,
                                   version=version)
 
@@ -659,7 +659,7 @@
     The nodes in common might not all be known locally due to the way the
     current discovery protocol works.
     """
-    outgoing = _computeoutgoing(repo, heads, common)
+    outgoing = computeoutgoing(repo, heads, common)
     return getlocalchangegroup(repo, source, outgoing, bundlecaps=bundlecaps)
 
 def changegroup(repo, basenodes, source):