compiler: Accept numeric literals with leading zeroes.

compiler: Accept numeric literals with leading zeroes.

    When a numeric literal with leading zeroes was seen in the parser, it
    would only be accepted if it were a valid hex or octal literal.  Any
    invalid numeric literal would be split up into multiple tokens: the
    valid hex/octal literal followed by the rest of the characters.
    Instead, when scanning a numeric literal with leading zeroes, always
    accept the number and give an appropriate error if the accepted number
    does not fit in the expected base.

    Fixes golang/go#11532, golang/go#11533.

    Reviewed-on: https://go-review.googlesource.com/13791

From-SVN: r227193