managen: output leading tabs for 8 spaces

This replacing of eight leading spaces into tabs was already done for
the embedded uncompressed version in tool_hugehelp.c so it does not save
anything there. But the gzip compressed version ends up almost 2K
smaller.

The output in a terminal should be identical.

Before using TABs:

curl.txt 282492 bytes
curl.txt.gz 73261 bytes

With this change applied:

curl.txt 249382 bytes
curl.txt.gz 71470 bytes