change default strftime format for better portability

On some systems, such as Solaris and HP-UX, "%c" format
give output without the leading zero on the single-digit
month-day.

mercurial/util.py

@@ -742,7 +742,7 b' def makedate():'
         tz = time.timezone
     return time.mktime(lt), tz
 
-def datestr(date=None, format='%c'):
+def datestr(date=None, format='%a %b %d %H:%M:%S %Y'):
     """represent a (unixtime, offset) tuple as a localized time.
     unixtime is seconds since the epoch, and offset is the time zone's
     number of seconds away from UTC."""

tests/test-remove

@@ -8,10 +8,10 b' hg commit -m 1 -d "1000000 0"'
 rm foo
 hg remove foo
 hg commit -m 2 -d "1000000 0"
-hg export 0 | sed -e "s/Thu Jan 01/Thu Jan  1/"
-hg export 1 | sed -e "s/Thu Jan 01/Thu Jan  1/"
-hg log -p -r 0 | sed -e "s/Thu Jan 01/Thu Jan  1/"
-hg log -p -r 1 | sed -e "s/Thu Jan 01/Thu Jan  1/"
+hg export 0
+hg export 1
+hg log -p -r 0
+hg log -p -r 1
 
 cd ..
 hg clone a b

tests/test-remove.out

@@ -5,7 +5,7 b''
 1
 
 diff -r 000000000000 -r 8ba83d44753d foo
---- /dev/null	Thu Jan  1 00:00:00 1970 +0000
+--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
 +++ b/foo	Mon Jan 12 13:46:40 1970 +0000
 @@ -0,0 +1,1 @@
 +a
@@ -17,7 +17,7 b' 2'
 
 diff -r 8ba83d44753d -r a1fce69c50d9 foo
 --- a/foo	Mon Jan 12 13:46:40 1970 +0000
-+++ /dev/null	Thu Jan  1 00:00:00 1970 +0000
++++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
 @@ -1,1 +0,0 @@
 -a
 changeset:   0:8ba83d44753d
@@ -26,7 +26,7 b' date: Mon Jan 12 13:46:40 1970 +0'
 summary:     1
 
 diff -r 000000000000 -r 8ba83d44753d foo
---- /dev/null	Thu Jan  1 00:00:00 1970 +0000
+--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
 +++ b/foo	Mon Jan 12 13:46:40 1970 +0000
 @@ -0,0 +1,1 @@
 +a
@@ -40,7 +40,7 b' summary: 2'
 
 diff -r 8ba83d44753d -r a1fce69c50d9 foo
 --- a/foo	Mon Jan 12 13:46:40 1970 +0000
-+++ /dev/null	Thu Jan  1 00:00:00 1970 +0000
++++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
 @@ -1,1 +0,0 @@
 -a