merged branch jonathaningram/patch-1 (PR #549)

Commits
-------

989bb22 Removed trailing white spaces
f880bab Help the developer when they specify an invalid filter by providing some alternatives

Discussion
----------

Help the developer when they specify an invalid filter by providing some...

... alternatives.

Bug fix: no
Feature addition: yes
Backwards compatibility break: no

Uses a simple `strpos` search (no fancy diff to determine what the filter could be). There is no impact to runtime performance because this is all happening during template compilation.

Examples:

```jinja
{{ my_entity|json }}
```

Shows exception:

`The filter "json" does not exist. Did you mean "json_encode"?`

```jinja
{{ my_date|dat }}
```

Shows:

`The filter "dat" does not exist. Did you mean "date"?`

```jinja
{{ my_var|f }}
```

Shows:

`The filter "f" does not exist. Did you mean "format", "default", "_default", "format_args", "format_args_as_text", "file_excerpt", "format_file", "format_file_from_text", "file_link"?`

Also good for custom filters created in your own domain `st_`:

```jinja
{{ my_var|st_ }}
```

Shows:

`The filter "st_" does not exist. Did you mean "st_friendly_date", "st_site_test_url"?`

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by stof at 2011/12/04 16:34:27 -0800

I like the idea to provide help to the developer in case of error. You should probably do the same for functions

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by Tobion at 2011/12/05 05:56:29 -0800

+1 for a combination of string starts with (suggesting domain specific filters, e.g. st_*) and levenshtein for typos

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by chucktrukk at 2011/12/05 08:13:10 -0800

+1. This would be really helpful.