Use C99 flexible array in pool.c

Refactoring mruby-random

Add kernel#rand, #srand ,Random#rand, #srand method

fix build error on VS2012 toolchains.

Cleanup code.

remove unused functions 'mrb_strerrno' and 'mrb_bug_errno'.

Reduce stdio dependency

Fix indentation in mirb.c

mruby-sprintf should precede mruby-print

Make topenv() static inlined to avoid compiling error when using clang and -O0 mode

Changed the RData type field to 'const'

Adjusted indent, space and tab

Include stddef.h. It is required by size_t. In case you include stdio.h, stddef.h is included indirectly.

Within the mruby source code the 'type' field is either initialized, or used in const manner.
IMHO changing the type after it has been created might cause hard to track errors.