BUG #11882: make HAVE_WORKING_LINK an option

The following bug has been logged on the website:

Bug reference:      11882
Logged by:          david gauchard
Email address:      gauchard@laas.fr
PostgreSQL version: 9.4beta2
Operating system:   linux
Description:

Hi,

This define "HAVE_WORKING_LINK" should not be always enabled. On systems
that support (and surely use) hard links FS, postgresql might be used on a
subFS not supporting it.
In the sources, the comment is (from git's
src/backend/access/transam/xlog.c):

3373      * Prefer link() to rename() here just to be really sure that we
don't
3374      * overwrite an existing logfile.  However, there shouldn't be one,
so
3375      * rename() is an acceptable substitute except for the truly
paranoid.

My thinking is that you may add a '--paranoid' option to use hardlink
instead of rename, or, at least, an option (--relax ?) to disable this
behaviour and use a regular rename() instead.

Just a thought.

david