MSSQL: Parse IF/ELSE without semicolon delimiters

[yoavcloud]

When parsing a SQL that doesn't use semicolon delimiters, for example:

SELECT col FROM tbl
IF x=1
  SELECT 1
ELSE
  SELECT 2

The parser needs to identify the IF keyword as a new statement instead of an alias for tbl and the ELSE as part of the conditional statement instead of an alias to 1. Moreover, MSSQL doesn't support IF/ELSE as explicit (after AS) or implicit table or column aliases.

Removed the assumption that every keyword after AS is an alias, and extended MSSQL to exclude IF/ELSE as alias.

[iffyio]

LGTM! Thanks @yoavcloud!