Fixes bug in ActiveRecord::QueryMethods, #1697

[jaw6]

Replace split on comma with a regexp that will reverse all ASC/DESC specifically
#1697 says it was fixed, but that fix was reverted in 971a74b. It seems likely 18d307e was failing on Travis because MAX (the function used in the test scenario) does not actually accept multiple arguments on MySQL.

[titanous]

It looks like this patch is also ~37% faster than the previous implementation on Ruby 1.9:

ruby 1.9.3dev (2011-07-31 revision 32789) [x86_64-darwin11.0.0]
Rehearsal ---------------------------------------
old   0.080000   0.000000   0.080000 (  0.079311)
new   0.050000   0.000000   0.050000 (  0.047826)
------------------------------ total: 0.130000sec

          user     system      total        real
old   0.070000   0.000000   0.070000 (  0.077106)
new   0.040000   0.000000   0.040000 (  0.046636)

ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin11.0.0]
Rehearsal ---------------------------------------
old   0.080000   0.000000   0.080000 (  0.080773)
new   0.050000   0.000000   0.050000 (  0.049190)
------------------------------ total: 0.130000sec

          user     system      total        real
old   0.080000   0.000000   0.080000 (  0.080600)
new   0.040000   0.000000   0.040000 (  0.048524)

ruby 1.8.7 (2011-02-18 patchlevel 334) [i686-darwin11.0.0], MBARI 0x6770, Ruby Enterprise Edition 2011.03
Rehearsal ---------------------------------------
old   0.100000   0.000000   0.100000 (  0.100959)
new   0.090000   0.000000   0.090000 (  0.096180)
------------------------------ total: 0.190000sec

          user     system      total        real
old   0.100000   0.000000   0.100000 (  0.099736)
new   0.100000   0.000000   0.100000 (  0.093022)

Benchmark source