Bug 14522: Use Koha::Cache for accessing single_holidays()

Bug 14522: Use Koha::Cache for accessing single_holidays()

this patch adds Koha::Cache functionality to the 'single_holidays' table
it is a performance patch for the problem described in BZ14315, only

 http://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=14315

it replaces slooow DateTime holiday objects with simple Ymd strings (19991230), then stores the strings in an @array using Koha::Cache
it does not attempt to add caching to all holiday tables - just the single_holidays table (at this stage

 on my test (master-cd9a827); nytprof showed a time reduction of the single_holidays() sub - from 61.7s to 587ms

here are some before/after nytprof runs, (really on master-cd9a827, not 3.20)

 http://x1.kohaaloha.com/i/nyt-bz14522-before/home-mason-g-k-3-20-x-Koha-Calendar-pm-1485-line.html#237
 http://x1.kohaaloha.com/i/nyt-bz14522-after/home-mason-g-k-3-20-x-Koha-Calendar-pm-1485-line.html#280

to test...

1/ add a bunch of single_holidays to your test koha, (my table has 400 holiday rows)
2/ add a loong circ rule for an itemtype (my rule has 140 days)
3/ checkout an item to a user (took me 67 secs)

apply patch...
4/ return item
5/ repeats steps 1..3, (took me 6 secs)

6/ add/change/delete some various single_holidays, via Home->Tools->Calendar
    ensure that your various changes have indeed saved correctly

for extra points...

7/ run tests t/Calendar.t and t/db_dependent/Holidays.t, with all tests pass OK

 sudo  koha-shell -c '  export PERL5LIB=/home/mason/g/k/master ; \
 cd /home/mason/g/k/master ;  perl  t/Calendar.t ; perl  t/db_dependent/Holidays.t  '   testkoha

8/ run QA tool, with all tests pass OK

 sudo  koha-shell -c ' \
export KOHA_CONF=/etc/koha/sites/mayo2/koha-conf.xml \
 export PERL5LIB=/home/mason/g/k/master:/home/mason/qa-test-tools/ ; \
 cd /home/mason/g/k/master ;   perl /home/mason/qa-test-tools/koha-qa.pl  -c 1 ' testkoha

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>