(build) Let Travis CI restore packages first

In the documentation (http://docs.travis-ci.com/user/languages/csharp/#NuGet)
Travis CI should restore nuget packages automatically with the keyword
solution. Script overrides xbuild and performs the build action requested
instead. This ensures that packages have been restored already for
compile.pre.step.

.build/compile.step

@@ -113,7 +113,7 @@
           commandline="${solution.path} /nologo /property:OutputPath='${msbuild.outputpath}' /property:Configuration=${msbuild.configuration} /verbosity:minimal /noconsolelogger /target:Clean" if="${microsoft.framework.specific != 'mono-4.0'}" />
       <echo level="Warning" message="Building..." />
       <echo level="Warning" message="Working directory ${dirs.build}" />
-      <echo level="Warning" message="Running ${app.xbuild} ${solution.path} /nologo /property:OutputPath='${msbuild.outputpath}' /property:Configuration=${msbuild.configuration} /verbosity:detailed /toolsversion:${framework::get-version(microsoft.framework.specific)} /property:Platform='${msbuild.platform}' /property:TargetFrameworkProfile='' /property:TargetFrameworkVersion=v${framework::get-version(microsoft.framework.specific)} /l:${msbuild.logger};'${dirs.build_results}${path.separator}msbuild-${microsoft.framework.specific}-results.xml'" />
+      <echo level="Warning" message="Running ${app.xbuild} ${solution.path} /nologo /property:OutputPath='${msbuild.outputpath}' /property:Configuration=${msbuild.configuration} /verbosity:detailed /toolsversion:${framework::get-version(microsoft.framework.specific)} /property:Platform='${msbuild.platform}' /property:TargetFrameworkVersion=v${framework::get-version(microsoft.framework.specific)} /l:${msbuild.logger};'${dirs.build_results}${path.separator}msbuild-${microsoft.framework.specific}-results.xml'" />
       <exec program="${app.xbuild}"
           basedir="/usr/bin"
           workingdir="${dirs.build}"

.travis.yml

@@ -1,4 +1,5 @@
 language: csharp
+solution: src/chocolatey.sln
 install:
   - sudo apt-get install mono-devel mono-gmcs nunit-console
 before_script: