Notable changes:
- libmagic is no longer used at all. All MIME type detection is
done through new Bro signatures, and there's no longer a means to get
verbose file type descriptions (e.g. "PNG image data, 1435 x 170").
The majority of the default file magic signatures are derived
from the default magic database of libmagic ~5.17.
- File magic signatures consist of two new constructs in the
signature rule parsing grammar: "file-magic" gives a regular
expression to match against, and "file-mime" gives the MIME type
string of content that matches the magic and an optional strength
value for the match.
- Modified signature/rule syntax for identifiers: they can no longer
start with a '-', which made for ambiguous syntax when doing negative
strength values in "file-mime". Also brought syntax for Bro script
identifiers in line with reality (they can't start with numbers or
include '-' at all).
- A new Built-In Function, "file_magic", can be used to get all
file magic matches and their corresponding strength against a given
chunk of data
- The second parameter of the "identify_data" Built-In Function
can no longer be used to get verbose file type descriptions, though it
can still be used to get the strongest matching file magic signature.
- The "file_transferred" event's "descr" parameter no longer
contains verbose file type descriptions.
- The BROMAGIC environment variable no longer changes any behavior
in Bro as magic databases are no longer used/installed.
- Reverted back to minimum requirement of CMake 2.6.3 from 2.8.0
(it's back to being the same requirement as the Bro v2.2 release).
The bump was to accomodate building libmagic as an external project,
which is no longer needed.
Addresses BIT-1143.
