Fix Issue 1234.

Fix Issue 1234.

Ensure that there is always enough bytes between consequtive calls in
unoptimized code to write a call instruction at the return points
without overlapping.

This handles the case where two return points were only four bytes
apart (because the latter call was to a register).

BUG=v8:1234
Committed: http://code.google.com/p/v8/source/detail?r=7089

[Rico, 2011-03-08 10:25:37]

LGTM if we add a regression test.
In addition, are we sure that this never happens on ia32?
I think that we should assert that, if we believe so

[Lasse Reichstein, 2011-03-08 10:41:33]

We have an assertion in the deoptimizer.
It might be worth it to add checks to the code-generator, so that we can catch
the problem even if don't try to deoptimize.