This is an issue for fields whose name might be changed at any point, like any image ending in "jpeg" (which will be renamed to "jpg". That would cause the actual file to be saved to disk with ".jpeg", but be saved elsewhere as ".jpg".

This example (mostly copied from the example in `examples/forms/simple.py`) shows it better than I can explain:

    import os
    from flask import Flask
    from flask.ext.admin import Admin, form
    from flask.ext.admin.contrib import sqla
    from flask.ext.sqlalchemy import SQLAlchemy

    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///hello.db'
    db = SQLAlchemy(app)

    os.path.isdir('static') or os.mkdir('static')

    class Photo(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        path = db.Column(db.Unicode(128))

    class PhotoView(sqla.ModelView):
        form_extra_fields = {'path': form.ImageUploadField('Photo', base_path='static')}

    admin = Admin(app, 'Photos are broken!')
    admin.add_view(PhotoView(Photo, db.session))

    db.create_all()
    app.run(debug=True)

... try uploading files with `.jpeg` vs `.jpg` extensions. It's pretty broken.

_get_dir_url() may be called without a path

one positional instead of keyord parameter
gettext(gettext()) => gettext()

ONETOMANY should not be InputRequired.

Apply `type_formatter` after `column_formatter` in list view.

Added missing translation for 'save and continue'

prettify file size format

Apply Jinja2 filter "filesizeformat" to filesize values

Fix two small code error in examples.

Save form_overrides into CustomModelConverter, to fix #421, in conjunction with https://github.com/coleifer/wtf-peewee/pull/20

Inline model field fix to address issues #417, #418

Missing "op" alias for os.path

Use `send_file` instead of `send_from_directory` to serve files in FileAdmin

Don't use column name for pk

Gets the attribute name of the model's pk column, rather than the
column's name (which can differ).

This probably needs to happen for inherited keys, too, but I have not
tested.

The path is already validated in `_normalize_path`. Also, `send_from_directory` abort paths with backslash, breaking FileAdmin subfolders in Windows.

With `send_file`, we have a minor issue with the download URL, it has path with backslash, but `_normalize_path` fix this before download.

Make FileAdmin.base_url optional.