Rewrite manual to be gender-neutral.

Rewrite manual to be gender-neutral.

* doc/automake.texi (GNU Build System)
(Standard Directory Variables, General Operation, CVS)
(Hard-Coded Install Paths, Dependencies As Side Effects):
Rewrite text to not contain gender-specific pronouns when
speaking about developers or users, either by avoiding pronouns
or by addressing them as `you' instead.
* THANKS: Update.
Report by Christina Gratorp.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>