fix crash due to offsets being truncated to 32 bits.
opted to track offsets as 64 bits to allow for 64-bit address spaces
in userland.

recipe:
	ramfs -m /n/junk
	cp /bin/8c /n/junk
	>/dev/null dd -if /n/junk/8c -iseek 81191 -count 1 -bs 81191

Reference: /n/sources/patch/applied/ramfsvl
Date: Sun May  9 16:23:19 CES 2010
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ramfs.c	Sun May  9 16:20:09 2010
+++ /sys/src/cmd/ramfs.c	Sun May  9 16:20:08 2010
@@ -497,7 +497,7 @@
 {
 	Ram *r;
 	uchar *buf;
-	long off;
+	vlong off;
 	int n, m, cnt;
 
 	if(f->ram->busy == 0)
@@ -544,7 +544,7 @@
 rwrite(Fid *f)
 {
 	Ram *r;
-	ulong off;
+	uvlong off;
 	int cnt;
 
 	r = f->ram;