This reverts commits: 10d6a3aca7 8ba48c1b85 fba8627dc1 dd883de5ba
6c6a25feca 167e6b48f1 7cb96d41a5 3207979278 595b3c4fdd 1521f7cf89
c11c5e69ac cf33608203 3632a812c0 f56506be0d 86427a3219 .

The reason for the revert is that we observe ABA problem around
inline method cache.  When a cache misshits, we search for a
method entry.  And if the entry is identical to what was cached
before, we reuse the cache.  But the commits we are reverting here
introduced situations where a method entry is freed, then the
identical memory region is used for another method entry.  An
inline method cache cannot detect that ABA.

Here is a code that reproduce such situation:

```ruby
require 'prime'

class << Integer
  alias org_sqrt sqrt
  def sqrt(n)
    raise
  end

  GC.stress = true
  Prime.each(7*37){} rescue nil # <- Here we populate CC
  class << Object.new; end

  # These adjacent remove-then-alias maneuver
  # frees a method entry, then immediately
  # reuses it for another.
  remove_method :sqrt
  alias sqrt org_sqrt
end

Prime.each(7*37).to_a # <- SEGV
```

Now that we have eliminated most destructive operations over the
rb_method_entry_t / rb_callable_method_entry_t, let's make them
mostly immutabe and mark them const.

One exception is rb_export_method(), which destructively modifies
visibilities of method entries.  I have left that operation as is
because I suspect that destructiveness is the nature of that
function.

The latter is same as the former, removed the duplicate function.

Moving public headers was 12-years ago, no depend files would
expect ruby.h in the top source directory now.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67033 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

It wrongly used all linenos of ISeq#trace_points which includes not only
line events but also call, return, and other events.  So, the result
included some linenos that can not be covered at all by line coverage.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66468 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65196 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

This patch introduces "oneshot_lines" mode for `Coverage.start`, which
checks "whether each line was executed at least once or not", instead of
"how many times each line was executed".  A hook for each line is fired
at most once, and after it is fired, the hook flag was removed; it runs
with zero overhead.

See [Feature #15022] in detail.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65195 b2dd03c8-39d4-4d8f-98ff-823fe69b080e