lib-sieve: imap4flags extension: Forgot to check for empty flag/keyword in new flag checking function.

Added support for getting message part information and content.

Prevents useless jumps after break operation.

lib-sieve: Added support for having multiple instances of a single tag (type) within a single command.

Would not occur in Pigeonhole itself.

lib-sieve: mime extension: Fixed the header :mime :anychild test to work properly outside a foreverypart loop.

lib-sieve: message body: Fixed erroneous changes to the message part tree structure performed when re-parsing the message.

No duplicate check function was implemented, so that the discard action would be duplicated each time it is invoked.
This only affects the action limits (each discard invocation is counted as another new action).
The result of the script execution would be identical.

test suite: mime extension: Improved header test cases to catch header trimming and folding problems.

lib-sieve: message body: Fixed assert failure occurring when text extraction is attempted on a empty or broken text part.

lib-sieve: message body: Explicitly prevent attempting text extraction from header and multipart body parts.

This error can apparently occur if the program terminates earlier than the program client issues shutdown().

No final '\0' character was added to those body parts.
This occurs for the body test with the (default) `:text' body transform.

lib-sieve: code: Added assert to prevent emitting invalid byte code when extension definitions are wrong.