"make install" paths hardwired, prevents virtual install

Moin moin,

when you want to install the files at a different location than
specified as "run-time" path with "configure" (because you use
mounts, symlinks, ...), then this doesn't work:

	"make install prefix=real-path bindir=real-bin"

because the paths used for install are "hardcoded" by "configure"
in src/Makefile.in by using  <at> bindir <at>  rather than $(bindir) for the
INS_* vars.

See attached patch for what I mean.

Even better would be to have all the different destination paths
be dymanically assigned per
	prefix =  <at> prefix <at> 
	bindir = $(prefix)/...
	...
	INS_BINARY_DIR = $(bindir)

so that replacing either "prefix" to affect all vars or just
"bindir" for INS_BINARY_DIR can be overriden with "make install".

Ideally this would be good for TIN_DEFAULTS_DIR, too, but ...
unfortunately it doesn't use the standard "sysconfdir", which
isn't defined in that Makefile.in at all.

I'm no autotools expert, therefore I can't judge how complicated
it would be to make TIN_DEFAULTS_DIR in src/Makefile.in work