Update spec to 0.7. Remove obsolete/redundant rules for local variable initialization.

Update spec to 0.7. Remove obsolete/redundant rules for local variable initialization. Remove restriction on const instance creation. Liberalize type promotion rules.

R=rmacnak@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28589

[rmacnak, 2013-10-11 20:22:16]

lgtm

[gbracha, 2013-10-12 00:43:17]

Lasse & Johnni, please take a look at the changes to type promotion.

[Johnni Winther, 2013-10-14 07:23:34]

https://codereview.chromium.org/27054005/diff/9001/docs/language/dartLangSpec...
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/27054005/diff/9001/docs/language/dartLangSpec...
docs/language/dartLangSpec.tex:4370: It is pointless to deduce a weaker type
than what is already known. Furthermore, this would lead to a situation where
multiple types are associated with a variable at a given point, which
complicates the specification. Hence the requirement that $T << S$ (we use $<<$
rather than subtyping because subtyping is not a partial order).
It is not only weaker (less specific) types that leads to multiple types being
associated with a variable. Unrelated types also introduce it:

class I {}
class J {}

Object o = ...
if (o is I && o is J) {
  // o should now be known to have both type I and J.
}

[gbracha, 2013-10-14 16:37:55]

Committed patchset #3 manually as r28589 (presubmit successful).