syntax: improve allocation of escape_into

This causes escape_into to reserve capacity instead of having escape do
it. This is a bit more general and will benefit users of escape_into.

PR #655

regex-syntax/src/lib.rs

@@ -175,7 +175,7 @@ pub mod utf8;
 /// The string returned may be safely used as a literal in a regular
 /// expression.
 pub fn escape(text: &str) -> String {
- let mut quoted = String::with_capacity(text.len());
+ let mut quoted = String::new();
  escape_into(text, &mut quoted);
  quoted
 }
@@ -185,6 +185,7 @@ pub fn escape(text: &str) -> String {
 /// This will append escape characters into the given buffer. The characters
 /// that are appended are safe to use as a literal in a regular expression.
 pub fn escape_into(text: &str, buf: &mut String) {
+ buf.reserve(text.len());
  for c in text.chars() {
  if is_meta_character(c) {
  buf.push('\\');