Embed handlers for the audio and video shortcodes are too permissive

[kovshenin]

The regex patterns in the audio and video embed handlers introduced in [23729], do not contain the beginning and end of string markers (^ and $) and will thus match things such as:

http://example.org/wp-content/uploads/directory.mp3/file.php

Not a big deal, but it probably shouldn't.

[SergeyBiryukov]

Shouldn't wp_audio_embed() and wp_video_embed() handlers registration be moved to wp_maybe_load_embeds()?
​http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/media.php#L1074

[kovshenin]

In 24092.2.diff​:

• Add the pattern start/end markers
• Per @SergeyBiryukov move registration to wp_maybe_load_embeds
• Rename both handler functions to match the wp_embed_handler_* pattern
• Move handler functions closer to wp_embed_handler_googlevideo

[SergeyBiryukov]

In 24000:

• Add start/end markers to the regex patterns in audio and video embed handlers.
• Move the handler functions registration to wp_maybe_load_embeds().
• Rename both functions to match the wp_embed_handler_* pattern.
• Move the functions closer to wp_embed_handler_googlevideo().

props kovshenin. fixes #24092.