Changing what's escaped when printing.

With this patch the model is:

    - "print" cleans the data so that non-printable characters get
      escaped. This is not necessarily reversible.

    - to print in a reversible way, one can go through
      escape_string(); this escapes backslashes as well to make the
      decoding non-ambigious.

    - Logging always escapes similar to escape_string(), making it
      reversible.

Compared to master, we also change the escaping as follows:

    - We now only escape with "\xXX", no more "^X" or "\0". Exception:
      backslashes.

    - We escape backlashes as "\\".

    - There's no "alternative" output style anymore, i.e., fmt() '%A'
      qualifier is gone.

Baselines in testing/btest are updated, external tests not yet.

Addresses BIT-1333.

src/Desc.h

@@ -17,7 +17,6 @@ typedef enum {
 
 typedef enum {
 	STANDARD_STYLE,
-	ALTERNATIVE_STYLE,
 	RAW_STYLE,
 } desc_style;