Get the Mono build script working again.

The solution as a whole doesn't build yet - we probably want to remove
ProtoDump and ProtoMunge entirely, and ProtoBench should use Jan's new
benchmarks for parity with Java.

The version of NUnit on my machine, packaged with Mono 3.12.1, is
only NUnit 2.4.2, which is extremely old - it still requires an explicit
[TestFixture] attribute on test fixtures. I've added one just for ByteStringTest
for the moment so that we can see some tests passing in Travis, but as part of
a separate PR we should work on making sure we're using a recent NUnit version.
(It may already be doing so, but we can check that once it's working and merged.)

csharp/buildall.sh

@@ -11,12 +11,13 @@ SRC=$(dirname $0)/src
 
 set -ex
 
-echo Building the solution.
-xbuild /p:Configuration=$CONFIG $SRC/ProtocolBuffers.sln
+# echo Building the solution.
+# TODO(jonskeet): Re-enable building the whole solution when we have ProtoBench et al
+# working again.
+# xbuild /p:Configuration=$CONFIG $SRC/ProtocolBuffers.sln
 
-echo Running tests.
-$NUNIT_CONSOLE $SRC/ProtocolBuffers.Test/bin/$CONFIG/Google.ProtocolBuffers.Test.dll
-
-$NUNIT_CONSOLE $SRC/ProtocolBuffersLite.Test/bin/$CONFIG/Google.ProtocolBuffersLite.Test.dll
+xbuild /p:Configuration=$CONFIG $SRC/ProtocolBuffers/ProtocolBuffers.csproj
+xbuild /p:Configuration=$CONFIG $SRC/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
 
-$NUNIT_CONSOLE $SRC/ProtocolBuffersLite.Test/bin/$CONFIG/Google.ProtocolBuffersMixedLite.Test.dll
+echo Running tests.
+$NUNIT_CONSOLE $SRC/ProtocolBuffers.Test/bin/$CONFIG/Google.Protobuf.Test.dll

csharp/src/ProtocolBuffers.Test/ByteStringTest.cs

@@ -40,6 +40,7 @@ using NUnit.Framework;
 
 namespace Google.Protobuf
 {
+    [TestFixture]
     public class ByteStringTest
     {
         [Test]

csharp/src/ProtocolBuffers.sln

@@ -4,8 +4,6 @@ VisualStudioVersion = 14.0.22823.1
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ProtocolBuffers", "ProtocolBuffers\ProtocolBuffers.csproj", "{6908BDCE-D925-43F3-94AC-A531E6DF2591}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ProtocolBuffers.Serialization", "ProtocolBuffers.Serialization\ProtocolBuffers.Serialization.csproj", "{231391AF-449C-4A39-986C-AD7F270F4750}"
-EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ProtocolBuffers.Test", "ProtocolBuffers.Test\ProtocolBuffers.Test.csproj", "{DD01ED24-3750-4567-9A23-1DB676A15610}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "AddressBook", "AddressBook\AddressBook.csproj", "{A31F5FB2-4FF3-432A-B35B-5CD203606311}"
@@ -26,10 +24,6 @@ Global
 		{6908BDCE-D925-43F3-94AC-A531E6DF2591}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6908BDCE-D925-43F3-94AC-A531E6DF2591}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{6908BDCE-D925-43F3-94AC-A531E6DF2591}.Release|Any CPU.Build.0 = Release|Any CPU
-		{231391AF-449C-4A39-986C-AD7F270F4750}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{231391AF-449C-4A39-986C-AD7F270F4750}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{231391AF-449C-4A39-986C-AD7F270F4750}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{231391AF-449C-4A39-986C-AD7F270F4750}.Release|Any CPU.Build.0 = Release|Any CPU
 		{DD01ED24-3750-4567-9A23-1DB676A15610}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{DD01ED24-3750-4567-9A23-1DB676A15610}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DD01ED24-3750-4567-9A23-1DB676A15610}.Release|Any CPU.ActiveCfg = Release|Any CPU