Double NARGS

I just ran a simple one-liner[1] to find the average filepath
length on my system (absolute paths) and that came up with a value
~90 characters.  Assume this is out by a factor of two, we still
have potentially 5000 more arguments that we can put into the buffer.

Surely one might run xargs(1) on something that is not a filename.
We just choose to accomodate the common use-case as much as possible.

[1] find / 2>/dev/null | awk '{print length($0)}' \
	| awk '{a+=$1}END{print "average filepath length: ",a/NR}'

xargs.c

@@ -9,7 +9,7 @@
 #include "util.h"
 
 enum {
-	NARGS = 5000
+	NARGS = 10000
 };
 
 static int inputc(void);