Tests and fixes for (pre)parse errors related to future reserved words.

This contains the following fixes:
- PreParser was using an error "reserved_word" which doesn't exist in
messages.js. Changed it to "unexpected_reserved".

BUG=3126
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/153793002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19076 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Tests for (pre)parse errors when "yield" is found in inappropriate places.

In addition:
- Fix: PreParser used to report an unexpected token one token too late when
ParsePrimaryExpression failed.
- Unified identifier handling (PreParser::GetIdentifier is now like Parser::GetIdentifier).
- Fix: PreParser used to produce "unexpected_token YIELD" errors when Parser
produced "unexpected_token_identifier"; fixed PreParser to match Parser.

BUG=3126
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/151103006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19082 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'