SeaMonkey 2.15 Beta 2

# Fixes
- Not detecting feed when type has leading and/or trailing whitespace.
- The Select Addresses dialog came up blank if opened from a Compose window with a single To/Cc/Bcc field filled in.
- A change to the User Agent string has been reverted since it caused some website incompatibilities.
- Information failed to show on the message header pane under certain circumstances.
- The display quality of fonts could be perceived as bad when Cleartype was turned off on Windows.
- The permissions database was not read completely if it included an invalid entry.
- @supports has been disabled for now.