updates:
 - port to new icaltimezone_get_builtin_tzdata()
 - fix a few tests hidden by ADD_TESTS_REQUIRING_INVESTIGATION macro
 - eliminate compiler warnings
set use_builtin_tzdata according to the USE_BUILTIN_TZDATA build option

this way we keep backward compatibility to users expecting the
library to be built to use builtin tzdata by default. the calling
program can change this behavior with icalteimzone_set_builtin_tzdata(1)
fix build on Windows with MSVC 2012 due to new external symbols
for icaltimezone_(get|set)_builtin_tzdata
Eliminate many compiler warnings from gcc
eliminate more gcc compiler warnings, from test programs
Eliminate many compiler warnings from clang
eliminate compiler warnings found by gcc on Cygwin
pass ints to ctype functions
new _unused() macro to deal with unused arguments
as MSVC doesn't like the void trick.
fix compiler warnings truncating integer values found with MSVC
add back more tests that been hiding for some reason.
tests run again on Windows now
unleash and repair a bunch of tests that now work on Linux at least.
still need to test other platforms
fixup testing on Cygwin
remove unused consts, as found using clang 3.4 (on Travis)
Merge branch 'master' into coverity_scan