PATCH: Incorrect overwrite behaviour in cmdutils/tee

Created an attachment (id=5973)
corrects overwrites in cmdutils/tee

When executing tee,
it doesn't truncate output files before writing.

Example:
<name> <size>
file1 100
file2 300

cat file1 | tee file2

Result:
file1 100
file2 300 (100 first bytes overwritten by contents of file1).

must be:
file1 100
file2 100

In NT and UNIX versions of tee truncation is implemented.
Also POSIX-2001 standard tells that standard input
must be copied to each of the files, including stdout (truncate and write).

I've attached diff-patch.