[m-rev.] diff: Highlight some more keywords in Vim.

[Peter Wang]

vim/syntax/mercury.vim:
	Recognise `promise_impure', `promise_equivalent_solutions',
	`promise_equivalent_solution_sets', `arbitrary'.

diff --git a/vim/syntax/mercury.vim b/vim/syntax/mercury.vim
index b2e28c8..9d9ca40 100644
--- a/vim/syntax/mercury.vim
+++ b/vim/syntax/mercury.vim
@@ -123,6 +123,7 @@ syn keyword mercuryForeignMod   will_not_throw_exception
 syn keyword mercuryForeignMod   terminates
 
 syn keyword mercuryPurity       impure
+syn keyword mercuryPurity       promise_impure
 syn keyword mercuryPurity       promise_pure
 syn keyword mercuryPurity       promise_semipure
 syn keyword mercuryPurity       semipure
@@ -134,6 +135,8 @@ syn keyword mercuryLogical      semidet_fail semidet_false
 syn keyword mercuryLogical      semidet_succeed semidet_true
 syn keyword mercuryLogical      some all not
 syn keyword mercuryLogical      try catch catch_any
+syn keyword mercuryLogical      promise_equivalent_solutions
+syn keyword mercuryLogical      promise_equivalent_solution_sets arbitrary
 
 syn keyword mercuryBool         yes no
 syn keyword mercuryOperator     div rem mod