./configure --help lists incorrect default install location

[chrismarx]

When you run ./configure --help, it says:

By default, `make install' will install all the files in
`/usr/local/bin', `/usr/local/lib' etc.  You can specify
an installation prefix other than `/usr/local' using `--prefix',
for instance `--prefix=$HOME'.

But installing the latest 3.4dev build (​http://postgis.net/stuff/postgis-2.4.0dev.tar.gz), the files are instead installed to "/usr/lib/postgresql/10/bin/"

Not much of a problem, it's still easy enough to find out where they went, but they're certainly not where the documention indicates-

[pramsey]

The files actually go into *two* locations. The liblwgeom files go into /usr/local and the postgresql files (postgis.so, extension control, etc) go into whatever pgsql install location pg_config returned. It's hard to describe in one line of help text...

[pramsey]

And, that help string is generated by autoconf, not us, while if you do manually set the --prefix we do try and give you a huge warning

dnl ===========================================================================
dnl Explain our prefix policy if necessary.
dnl ===========================================================================

if test "$prefix" != "NONE"; then
  AC_MSG_RESULT([------------------------------------------------------------------------])
  AC_MSG_RESULT([  WARNING: You have set the --prefix to '$prefix'. But we mostly    ])
  AC_MSG_RESULT([  ignore the --prefix. For your info, using the values determined from ])
  AC_MSG_RESULT([  $PG_CONFIG we will be installing:   ])
  AC_MSG_RESULT([    * postgis shared library in $PGSQL_LIBDIR ])
  AC_MSG_RESULT([    * postgis SQL files in $PGSQL_SHAREDIR/contrib/postgis-$POSTGIS_MAJOR_VERSION.$POSTGIS_MINOR_VERSION ])
  AC_MSG_RESULT([    * postgis executables in $PGSQL_BINDIR ])
  AC_MSG_RESULT([------------------------------------------------------------------------])
fi