Corrected BNF input documentation for fast-import.

Now that fast-import uses uintmax_t (the largest available unsigned
integer type) for marks we don't want to say its an unsigned 32
bit integer in ASCII base 10 notation.  It could be much larger,
especially on 64 bit systems, and especially if a frontend uses
a very large number of marks (1 per file revision on a very, very
large import).
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -72,6 +72,7 @@ Format of STDIN stream:
   path_str    ::= path    | '"' quoted(path)    '"' ;
 
   declen ::= # unsigned 32 bit value, ascii base10 notation;
+  bigint ::= # unsigned integer value, ascii base10 notation;
   binary_data ::= # file content, not interpreted;
 
   sp ::= # ASCII space character;
@@ -81,7 +82,7 @@ Format of STDIN stream:
 	 # an idnum.  This is to distinguish it from a ref or tag name as
      # GIT does not permit ':' in ref or tag strings.
 	 #
-  idnum   ::= ':' declen;
+  idnum   ::= ':' bigint;
   path    ::= # GIT style file path, e.g. "a/b/c";
   ref     ::= # GIT ref name, e.g. "refs/heads/MOZ_GECKO_EXPERIMENT";
   tag     ::= # GIT tag name, e.g. "FIREFOX_1_5";