Fix &raw_output and enable_raw_output interpretation of NUL characters

When using a `print` statement to write to a file that has raw output
enabled, NUL characters in string are no longer interpreted into "\0",
no newline is appended afterwards, and each argument to `print` is
written to the file without any additional separation.

(Re)Assigning to identifiers with the &raw_output attribute should also
now correctly apply the attribute to the file value being assigned.

Note that the write_file BiF should already be capable of raw string
data to a file, expect it bypasses the print_hook event.

Addresses #474

src/Desc.h

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