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templater: take any string literals as template, but not for rawstring (BC)

This patch series is intended to unify the interpretation of string literals.
It is breaking change that boldly assumes

 a. string literal "..." never contains template-like fragment or it is
    intended to be a template
 b. we tend to use raw string literal r"..." for regexp pattern in which "{"
    should have different meaning

Currently, we don't have a comprehensible rule how string literals are
evaluated in template functions. For example, fill() takes "initialindent"
and "hangindent" as templates, but not for "text", whereas "text" is a
template in pad() function.

  date(date, fmt)
  diff(includepattern, excludepattern)
  fill(text, width, initialident: T, hangindent: T)
  get(dict, key)
  if(expr, then: T, else: T)
  ifcontains(search, thing, then: T, else: T)
  ifeq(expr1, expr2, then: T, else: T)
  indent(text, indentchars, firstline)
  join(list, sep)
  label(label: T, expr: T)
  pad(text: T, width, fillchar, right)
  revset(query, formatargs...])
  rstdoc(text, style)
  shortest(node, minlength)
  startswith(pattern, text)
  strip(text, chars)
  sub(pattern, replacement, expression: T)
  word(number, text, separator)
  expr % template: T

  T: interpret "string" or r"rawstring" as template

This patch series adjusts the rule as follows:

 a. string literal, '' or "", starts template processing (BC)
 b. raw string literal, r'' or r"", disables both \-escape and template
    processing (BC, done by subsequent patches)
 c. fragment not surrounded by {} is non-templated string

  "ccc{'aaa'}{r'bbb'}"
   ------------------  *: template
   ---                 c: string
        ---            a: template
                ---    b: rawstring

Because this can eliminate the compilation of template arguments from the
evaluation phase, "hg log -Tdefault" gets faster.

  % cd mozilla-central
  % LANG=C HGRCPATH=/dev/null hg log -Tdefault -r0:10000 --time > /dev/null
  before: real 4.870 secs (user 4.860+0.000 sys 0.010+0.000)
  after:  real 3.480 secs (user 3.440+0.000 sys 0.030+0.000)

Also, this will allow us to parse nested templates at once for better error
indication.

Mercurial
=========

Mercurial is a fast, easy to use, distributed revision control tool
for software developers.

Basic install:

 $ make            # see install targets
 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

Running without installing:

 $ make local      # build for inplace usage
 $ ./hg --version  # should show the latest version

See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.