upgrade old {UNIT} macro to 1.4's {LOYAL_UNIT}

Of course, during 1.5, this macro was renamed to {*NAMED_*LOYAL_UNIT}, but we will stick to upgrading to "1.4", and worry about changing LOYAL_UNIT to NAMED_LOYAL_UNIT in the current wmllint.

The basic "if '{UNIT '" condition is more efficient than subjecting every line to a complex regex. However, it would be theoretically possible for a matching line to fail the substitution. Thus, I used subn() instead of sub(), and only report an upgrade to stdout if there is at least one substitution. In the hypothetical case that no substitution is carried out, I alert the user so they can look into it.

The regular expression looks intimidating, so here's an explanation:

field 1: unit type - The authors of this era seem to have been pretty good about enclosing fields in parentheses, but this part of the regex accounts for all three possibilities: a) parentheses used to enclose; b) quotes used to enclose; c) no enclosure, thus ending with the next space.
field 2: id - Basically a clone of the first field.
field 3: name - Clone of the first two fields, except for allowing a translability underscore in the last two cases (though early UMC seems to all follow the practice of including the translatability underscore with the rest of the name inside parentheses.)
field 4: side - We can expect this to be a number. Old add-ons should all be using single digits, but I allow more than one digit to match anyway. In theory, there could be cases which would break the regex (e.g., enclosing the number in parentheses, a macro substitution), but since I don't know of any, I'll just call it a day.
field 5: x coordinate - Usually this will be a number, but it could also be a variable or a macro substitution.
field 6: y coordinate - Clone of field 6, except with y/Y substituted for x/X.

(A side note: after testing this commit, I noticed that the introduction to hack_syntax called for "set[ting] modcount to nonzero" when modifying lines, there are "modcount += 1" lines throughout the animation transformations, and hack_syntax ends with "return (lines, modcount)". Looking into it, however: a) my code was working fine without it, with no change detected after I tested inserting "modcount += 1"; b) I never figured out just what use wmllint was making of the modcount, despite all the care to increment it upwards; c) the last suite in hack_syntax doesn't use modcount, either, and it turns out to have been written by ESR himself in February 2008, after all the other code.)

data/tools/wmllint-1.4

@@ -1523,6 +1523,18 @@ start_time=-150
             in_terrain = False
         if in_terrain:
             lines[i] = lines[i].replace("letter", "terrain")
+    # Upgrade old UNIT macro to 1.4's LOYAL_UNIT
+    for i in range(len(lines)):
+        if "no-syntax-rewrite" in lines[i]:
+            break
+        if '{UNIT ' in lines[i]:
+            old = lines[i].strip()
+            (new, num) = re.subn(r'{UNIT +(\([^)]*\)|"[^"]*"|[^(" ][^ ]*) +(\([^)]*\)|"[^"]*"|[^(" ][^ ]*) +(\([^)]*\)|_? *"[^"]*"|_? *[^(" ][^ ]*) +([0-9]+) +([0-9]+|[^ ]*\$[^ ]*x[^ ]*|\(?{[A-Z0-9_]*X[A-Z0-9_]*}\)?) +([0-9]+|[^ ]*\$[^ ]*y[^ ]*|\(?{[A-Z0-9_]*Y[A-Z0-9_]*}\)?)}', r'{LOYAL_UNIT \4 \1 \5 \6 \2 \3}', lines[i])
+            if num > 0:
+                lines[i] = new
+                print '"%s", line %d: %s -> %s' % (filename, i+1, old, new.strip())
+            if num == 0:
+                print '"%s", line %d: UNIT macro not converted to LOYAL_UNIT (%s)' % (filename, i+1, old)
     # More syntax transformations would go here.
     return (lines, modcount)