Detection of SWIG and C# by configure

[szekerest]

This is the C# specific part for the following tracking bug:

http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=1720

The following issues should be considered for the C# binding

1. As the recent changes the C# binding currently have makefile.in template, and
configure.in was changed to create the corresponding makefile

2. The mono related documentation contains a skeleton project on how to detect
the C# compiler. The all stuff can be founded here:

http://www.mono-project.com/Guidelines:Application_Deployment

I have copied the C# compiler detection parts related to our demands here:

dnl C# compiler
AC_PATH_PROG(CSC, csc, no)
AC_PATH_PROG(MCS, mcs, no)
AC_PATH_PROG(MONO, mono, no)

CS="C#"
if test "x$CSC" = "xno" -a "x$MCS" = "xno"  ; then
	dnl AC_MSG_ERROR([You need to install a C# compiler])
	AC_MSG_ERROR([No $CS compiler found])
fi

if test "x$MCS" = "xno" ; then
	MCS=$CSC
fi

if test "x$MONO" = "xno"; then
	AC_MSG_ERROR([No mono runtime found])
fi

AC_SUBST(MCS)


3. Due to many of the breaking issues of SWIG currently the 1.3.27 or later
version is supported for the C# bindings.

Tamas