Working towards improving the handling of currupt binaries: defined multiple exit codes for execution functions and defined trace macro for reporting binary corruptions.

Fixed code emission for extension-defined variables and removed hardcoded paths from include extension.

Testsuite: tested handling of teststuite envelope environment and fixed bugs in the envelope test in the process.

Reversed stat() and open() on two occasions to make retrieved stat information guaranteed to be valid for the opened file and added error handling for various close() system calls.

Removed various unnecessary includes of <ctype.h> and replaced yey another toupper() with its i_* equivalent.

Removed direct use of isdigit, isalpha and isalnum and replaced these with their dovecot i_* equivalents to prevent problems on some systems.