Pacify MSVC warnings for numeric.c, proc.c, and symbol.c
Change mrblib's source path to absolute path
Merge pull request #2600 from mimaki/fix_msvc_warnings

Pacify MSVC warnings for numeric.c, proc.c, and symbol.c
cast MRB_ENV_STACK_LEN to (mrb_int); ref #2600
Merge pull request #2601 from mimaki/mrblib_absolute_path

Change mrblib's source path to absolute path
fixed. cygwin-gcc(ver4.8.3) warning in conv_digit()
remove accidental check-in of mruby-thread gem
Merge pull request #2602 from Hiroyuki-Matsuzaki/fix_cygwin_gcc_warning

fixed. cygwin-gcc(ver4.8.3) warning in conv_digit()
word_boxing.h used int to represent symbols; use mrb_sym instead
time_t may overflow mrb_int when word boxing is used
always check range before casting time_t to mrb_int
add similar range check for tm->usec as well
fix typo (i->idx)
Merge pull request #2608 from mrbrdo/fix-typo

fix typo (i->idx)
remove header prototype of mrb_exc_print; close #2607
context proc may be cfunc; fix #2609
need addtional type check to avoid SEGV; ref #2609
Add Kernel.Array
Merge pull request #2611 from suzukaze/add-kernel.Array

Add Kernel.Array
refactoring C part of #2611