Update extensions/README

[mwtoews]

Summary of changes included in the patch:

• reStructuredText Markup, 80 column text
• Rewrite several paragraphs
• Add requirements section
• Make it clear that --with-raster is required, and that postgis also includes the raster support

[strk]

--with-raster is the default now

[strk]

I think the explicit "make install" from within extensions/ should not be needed either, but rather "make install" from top-level build dir should do. Did you try ?

[mwtoews]

I recall sometimes seeing make install also build the extension, but not always. I just did a test --without-topology where the extension was not built.

The --with-raster comment is to imply that you cannot use --without-raster.

[robe]

strk -- correct make install from within extensions is not required. it will build if you are running PostgreSQL 9.1+. Or at least that is what pramsey changed. I'll have to double-check my make script to confirm I'm still not cding into the extension folders to build.

Do we still support a --with-raster? I though its just --without-raster now. guess it doesn't hurt to have both.

Mike did you agree to our terms of commit and aren't you one of us? If so feel free to commit this yourself. I admit I only remember agreeing to a +1 when pramsey brought you up for vote and then some discussion ensued that put me to sleep. When I woke up I wasn't sure what transpired.

[mwtoews]

I can confirm that the extensions do not always build; see: http://trac.osgeo.org/postgis/browser/trunk/configure.ac#L1053

The configure.ac logic requires all of these: >=91 AND xsltproc AND raster AND topology.

Comments are included with beta4.tar.gz, so xsltproc isn't needed. Also topology doesn't necessary need to be enabled to build the postgis extension. However, I can build these extensions without issues by cd'ing into extensions, make, make install.

I agree to the terms of committees, but I don't have any svn commit privileges. Here is the thread:  http://postgis.refractions.net/pipermail/postgis-devel/2012-February/thread.html#18515

[strk]

If it is possible to build extension w/out xsltproc and topology we should fix ./configure to allow that.

[strk]

Anyway, it's an improvement, so committed as r9555