shelve: move possible shelve file extensions to a single place

This and a couple of following patches are a preparation to
implementing obsolescense-enabled shelve which was discussed
on a Sprint. If this refactoring is not done, shelve is going
to look even more hackish than now.

This particular commit introduces a slight behavior change. Previously,
if only .hg/shelve/name.patch file exists, but .hg/name.hg does not,
'hg shelve -d name' would fail saying "shelve not found". Now deletion
will only fail if .patch file does not exist (since .patch is used
as an indicator of an existing shelve). Other shelve files being absent
are skipped silently to accommodate for future introduction of obs-based
shelve, which will mean that for some shelves .hg and .patch files exist,
while for others .hg and .oshelve.

hgext/shelve.py

@@ -62,6 +62,7 b" testedwith = 'ships-with-hg-core'"
 
 backupdir = 'shelve-backup'
 shelvedir = 'shelved'
+shelvefileextensions = ['hg', 'patch']
 
 class shelvedfile(object):
     """Helper for the file storing a single shelve
@@ -221,7 +222,7 b' def cleanupoldbackups(repo):'
             # keep it, because timestamp can't decide exact order of backups
             continue
         base = f[:-3]
-        for ext in 'hg patch'.split():
+        for ext in shelvefileextensions:
             try:
                 vfs.unlink(base + '.' + ext)
             except OSError as err:
@@ -399,7 +400,7 b' def cleanupcmd(ui, repo):'
     with repo.wlock():
         for (name, _type) in repo.vfs.readdir(shelvedir):
             suffix = name.rsplit('.', 1)[-1]
-            if suffix in ('hg', 'patch'):
+            if suffix in shelvefileextensions:
                 shelvedfile(repo, name).movetobackup()
             cleanupoldbackups(repo)
 
@@ -410,8 +411,15 b' def deletecmd(ui, repo, pats):'
     with repo.wlock():
         try:
             for name in pats:
-                for suffix in 'hg patch'.split():
-                    shelvedfile(repo, name, suffix).movetobackup()
+                for suffix in shelvefileextensions:
+                    shfile = shelvedfile(repo, name, suffix)
+                    # patch file is necessary, as it should
+                    # be present for any kind of shelve,
+                    # but the .hg file is optional as in future we
+                    # will add obsolete shelve with does not create a
+                    # bundle
+                    if shfile.exists() or suffix == 'patch':
+                        shfile.movetobackup()
             cleanupoldbackups(repo)
         except OSError as err:
             if err.errno != errno.ENOENT:
@@ -557,8 +565,10 b' def restorebranch(ui, repo, branchtorest'
 def unshelvecleanup(ui, repo, name, opts):
     """remove related files after an unshelve"""
     if not opts.get('keep'):
-        for filetype in 'hg patch'.split():
-            shelvedfile(repo, name, filetype).movetobackup()
+        for filetype in shelvefileextensions:
+            shfile = shelvedfile(repo, name, filetype)
+            if shfile.exists():
+                shfile.movetobackup()
         cleanupoldbackups(repo)
 
 def unshelvecontinue(ui, repo, state, opts):