mkXXXX: unify [KBYTES] parameter handling (added it to mkswap)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

include/libbb.h

@@ -412,6 +412,11 @@ int rename_or_warn(const char *oldpath, const char *newpath) FAST_FUNC;
 off_t xlseek(int fd, off_t offset, int whence) FAST_FUNC;
 off_t fdlength(int fd) FAST_FUNC;
 
+uoff_t FAST_FUNC get_volume_size_in_bytes(int fd,
+                const char *override,
+                unsigned override_units,
+                int extend);
+
 void xpipe(int filedes[2]) FAST_FUNC;
 /* In this form code with pipes is much more readable */
 struct fd_pair { int rd; int wr; };

include/usage.h

@@ -2844,7 +2844,7 @@
        "$ mknod -m 644 /tmp/pipe p\n"
 
 #define mkswap_trivial_usage \
-       "[OPTIONS] BLOCKDEV" /* [SIZE_IN_KB] */
+       "[OPTIONS] BLOCKDEV [KBYTES]"
 #define mkswap_full_usage "\n\n" \
        "Prepare BLOCKDEV to be used as swap partition\n" \
      "\nOptions:" \