.jshintrc

xdiff: reduce indent heuristic overhead

Adds some threshold to avoid expensive cases, like:

```
#!python
open('a', 'w').write(" \n" * 1000000)
open('b', 'w').write(" \n" * 1000001)
```

The indent heuristic is O(N * 20) (N = 1000000) for the above case, and
makes diff much slower.

Before this patch (system git 2.14.2):

```
git diff --no-indent-heuristic a b  0.21s user 0.03s system 100% cpu 0.239 total
git diff --indent-heuristic a b     0.77s user 0.02s system 99% cpu 0.785 total
```

After this patch (git 2fc74f41, with xdiffi.c patched):

```
# with the changed xdiffi.c
git diff --indent-heuristic a b      0.16s user 0.01s system 90% cpu 0.188 total
git diff --no-indent-heuristic a b   0.18s user 0.01s system 99% cpu 0.192 total
```

Now turning on indent-heuristic has no visible impact on performance.

Differential Revision: https://phab.mercurial-scm.org/D2601

{
    // Enforcing
    "eqeqeq"        : true,     // true: Require triple equals (===) for comparison
    "forin"         : true,     // true: Require filtering for..in loops with obj.hasOwnProperty()
    "freeze"        : true,     // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
    "nonbsp"        : true,     // true: Prohibit "non-breaking whitespace" characters.
    "undef"         : true,     // true: Require all non-global variables to be declared (prevents global leaks)

    // Environments
    "browser"       : true      // Web Browser (window, document, etc)
}