stream_wrap: don't call Number::New()

Replace call to Number::New() with a call to Integer::NewFromUnsigned().

Profiling a Real World(TM) application with perf(1) suggests that the
conversion of its argument from integer to double is disproportionally
costly: over 60% of CPU cycles accountable to WriteStringImpl() are
attributable to the conversion.

After changing it to Integer::NewFromUnsigned(), WriteStringImpl()
has dropped from the 'most costly functions' top ten altogether.
doc: http: properly document callback argument
doc: http: document ServerResponse 'finish' event
doc: net: fix typo in example code
build: include postmortem symbols on linux

Previously we were building the symbols, but the linker was garbage
collecting the symbols because they weren't used. Inform the linker
that we want to keep all symbols from v8 around.
Merge remote-tracking branch 'upstream/v0.10'

Conflicts:
	src/stream_wrap.cc