Optimize Syslog date rule using keywords in place of combinations

The previous rule used combinations of Day and Month three letter terms,
and was taking up about 30% of the syntax processing time.
The new methods using keywords has the side effect of highlighting the
three letter identifies in the whole file (they should be reasonably
rare outside of dates, however) but is much faster

Author: MTDL9

syntax/log.vim

@@ -43,8 +43,9 @@ syn region logString      start=/'\(s \|t \| \w\)\@!/ end=/'/ end=/$/ end=/s / s
 syn match logDate '\d\{2,4}[-\/]\(\d\{2}\|Jan\|Feb\|Mar\|Apr\|May\|Jun\|Jul\|Aug\|Sep\|Oct\|Nov\|Dec\)[-\/]\d\{2,4}T\?'
 " Matches 8 digit numbers at start of line starting with 20
 syn match logDate '^20\d\{6}'
-" Matches Fri Jan 09 or Feb 11 or Apr  3
-syn match logDate '\(\(Mon\|Tue\|Wed\|Thu\|Fri\|Sat\|Sun\) \)\?\(Jan\|Feb\|Mar\|Apr\|May\|Jun\|Jul\|Aug\|Sep\|Oct\|Nov\|Dec\) [0-9 ]\d'
+" Matches Fri Jan 09 or Feb 11 or Apr  3 or Sun 3
+syn keyword logDate Mon Tue Wed Thu Fri Sat Sun Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec nextgroup=logDateDay
+syn match logDateDay '\s\{1,2}\d\{1,2}' contained
 
 " Matches 12:09:38 or 00:03:38.129Z or 01:32:12.102938 +0700
 syn match logTime '\d\{2}:\d\{2}:\d\{2}\(\.\d\{2,6}\)\?\(\s\?[-+]\d\{2,4}\|Z\)\?\>' nextgroup=logTimeZone,logSysColumns skipwhite
@@ -112,6 +113,7 @@ hi def link logNull Constant
 hi def link logString String
 
 hi def link logDate Identifier
+hi def link logDateDay Identifier
 hi def link logTime Function
 hi def link logTimeZone Identifier