cache: create `cache` directory at init time

cache: create `cache` directory at init time

The cache directory will be needed very quickly, so it seems simpler to create
it early to make sure it has the same owner and permission than the other
directory in the repository.

--- a/mercurial/localrepo.py	Thu Nov 15 17:08:23 2018 +0100
+++ b/mercurial/localrepo.py	Thu Nov 15 02:38:55 2018 +0100
@@ -3010,6 +3010,8 @@
         wdirvfs.makedirs()
 
     hgvfs.makedir(notindexed=True)
+    if 'sharedrepo' not in createopts:
+        hgvfs.mkdir(b'cache')
 
     if b'store' in requirements and 'sharedrepo' not in createopts:
         hgvfs.mkdir(b'store')

--- a/tests/test-empty.t	Thu Nov 15 17:08:23 2018 +0100
+++ b/tests/test-empty.t	Thu Nov 15 02:38:55 2018 +0100
@@ -20,6 +20,7 @@
 
   $ ls .hg
   00changelog.i
+  cache
   requires
   store
 

--- a/tests/test-inherit-mode.t	Thu Nov 15 17:08:23 2018 +0100
+++ b/tests/test-inherit-mode.t	Thu Nov 15 02:38:55 2018 +0100
@@ -42,7 +42,7 @@
   $ hg init repo
   $ cd repo
 
-  $ chmod 0770 .hg/store
+  $ chmod 0770 .hg/store .hg/cache
 
 before commit
 store can be written by the group, other files cannot
@@ -51,6 +51,7 @@
   $ "$PYTHON" ../printmodes.py .
   00700 ./.hg/
   00600 ./.hg/00changelog.i
+  00770 ./.hg/cache/
   00600 ./.hg/requires
   00770 ./.hg/store/
 
@@ -116,6 +117,7 @@
   $ "$PYTHON" ../printmodes.py ../push
   00770 ../push/.hg/
   00660 ../push/.hg/00changelog.i
+  00770 ../push/.hg/cache/
   00660 ../push/.hg/requires
   00770 ../push/.hg/store/