Modify buffer size for filename.

Code formatting in sprintf.c

Also, fixed issue in Xcode project build settings

switch/case constructs in mrb_str_format() had mismatched indentation
styles: clean up to 2-spaces-per-level.

Canonicalize NaN value in NaN boxing environment

op_enter_optimize

Xcode project cleanup (corrects the error in #422, not pulled)

Now there are only three schemes (build commands, static library, OS X
framework) plus a scheme wrapping the standard make file.

`puts` should print "\n" only when the argument does not end with "\n".

Modify exception handling

If an exception is raised before cipush is called in mrb_run,
it should be handled in the outer mrb_run.

now segmented list can be used as instance variable tables by -DMRB_USE_IV_SEGLIST; we still need to measure the performance and memory consumption

Struct.new crashed if no parameters given. This pull request fixes that.