Defer the writing of the source position data to the relocation information

Defer the writing of the source position data to the relocation information
until a possible debug break location is reached. Currently this is call sites
with calls to code objects and JS return. Source position information in the
code therefore no longer refers to the "first" instruction generated for a
given source position (which was not the case defered code anyway) but to the
first break location after that source position was passed (again defered code
always start with source position information). This doesn't make a difference
for the debugger as it will always be stopped only at debug break locations.
However, this makes the life of the peep-hole optimizer much easier as many
oportunities for posh/pop eliminations where previosly blocked by relocation
information already written to the code object.

Two types of source positions are still collected. Statement positions indicate
the position of the start of the statement leading to this code and (plain)
positions indicate other places typically call sites to help indicate current
position in backtraces. The two different types of positions are also used to
distinguish between step next and step in.

Runs all the tests (including debugger tests) as before.

Moved the checking for the FLAG_debug_info to one place.

I will do the same changes to the ARM codegenerator in a seperate changelist.

Review URL: http://codereview.chromium.org/2957

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@335 ce2b1a6d-e550-0410-aec6-3dcde31c8c00