Linux build : Add sos flags and libxml2

[assefa]

For the Sensor support, modifications needed to build are :

 - libxml2 support (on windows libxml2-2.6.13 was tested)
 - add flag USE_OGC_SOS 
 - I have added mapogcsos.o in the makefile.in

[assefa]

adding tom in cc

[dmorissette]

Taking this one

[dmorissette]

To enable OGC SOS we will use "--with-sos". SOS will be disabled by default.

[dmorissette]

Assefa, what is the complete list of dependencies for SOS? Just libxml2 and
PROJ4? Do we need GDAL/OGR or others?

[dmorissette]

Assefa, the macro for WMS/WFS were -DUSE_WMS_SVR -DUSE_WFS_SVR, etc.

To be consistent, should we not use -DUSE_SOS_SVR instead of -DUSE_OGC_SOS?

[assefa]

I thought abaout it but since there is no sensor client (and it does not even
make sense to me that we would have it), I went with OGC_SOS. I guess we could
change it. I will do the changes in the source code and windows makefiles.
Please do the same for the linux one.

As for the dependent lib : libxml2 and proj. On windows, there might be a
dependency with iconv since the binaries that you download are built with it.

[dmorissette]

Even if the chances are low that we may implement SOS client connections some
day, I think it is better to be consistent with the way we name the compilation
flags.

My modifs to the configure.in and Makefiles are done. I'll wait for you to make
the changes to use -DUSE_SOS_SVR and then I'll test one more time and commit them.

[assefa]

I have updated cvs with the flags changes.

[dmorissette]

I have committed the configure.in and Makefile.in changes in CVS. Two new options:

   --with-sos              Enable OGC SOS Server Support (libxml2 required).
   --with-xml2-config=PATH Specify path to xml2-config.

If --with-sos is not specified then SOS is disabled by default. 

If libxml2 is located in the default system dirs then it should be detected
automatically, otherwise use --with-xml2-config to provide the path to the
xml2-config script.