[[:blank:]] does not just match [ \t]

[kennytm]

Both the docs of regex 1.0.5 and regex-syntax 0.6.2 suggests that [[:blank:]] is equivalent to [ \t], but it is actually wrong as shown in the test program below:

extern crate regex; // 1.0.5

fn main() {
    let r = regex::Regex::new("[[:blank:]]").unwrap();
    assert!(!r.is_match("\u{17}")); // unexpectedly panicked
}

I believe the error is due to

regex/regex-syntax/src/hir/translate.rs

Lines 1042 to 1045 in 488fe56

	Blank => {
	const X: T = &[(' ', '\t')];
	X
	}

line 1043 should read

 const X: T = &[('\t', '\t'), (' ', ' ')];