(1) unify similar functions (rb_backtrace_each() and
backtrace_object()). backtrace_each() is a unified function.
variation:
a) backtrace_object(): create backtrace object.
b) vm_backtrace_str_ary(): create bt as an array of string.
c) vm_backtrace_print(): print backtrace to specified file.
d) rb_backtrace_print_as_bugreport(): print backtrace on
bugreport style.
(2) remove rb_backtrace_each(). Use backtrace_each() instead.
(3) chang the type of lev parameter to size_t.
a) lev == 0 means current frame (exception, etc use it).
b) lev == 1 means upper frame (caller(0) use it).
* vm_core.h, vm_dump.c, vm_eval.c: ditto.
* vm.c (backtrace_object(), vm_backtrace_str_ary()): fix to return a
correct size of caller(lev) array.
Let n be a "caller(0).size" then ln as caller(lev).size should be
(n - lev). However, the previous implementation returns a wrong
size array (ln > n - lev). [ruby-dev:45673]
* test/ruby/test_backtrace.rb: add tests for backtrace.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@35787 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
