Merge pull request #2142 from cremno/rename-mrb_str_buf_append

rename `mrb_str_buf_append` to `mrb_str_cat_str`
presreve local variables names in irep->lv
better codedump formatting
enable bintest on TravisCI to see how it works
prevent printf warning
add post mandatory argument test
Merge pull request #2143 from mirichi/test

add post mandatory argument test
fix OP_BLKPUSH dump format
should care about the case that given arguments are less then mandatory formal arguments and optional arguments exist; close #2144
Speed up Array#select! from O(n^2) to O(n).
Print file name and line number in codedump if available.
Use int32_t as line variable type.
make peek_n append p->pb to list
Accept =begin and =end with spaces after
Add tests for multiline comment parsing
clear ci->proc to prevent GC crash
fiber context may be NULL
stack may be uncleared
clear all stack everytime to prevent GC crash; ref #2109
cast intptr_t to mrb_int to pacify compiler warning; close #2148