Merge branch 'appveyor-tests'

Fix several problems in tests under MSW (mostly with MinGW) and enable
building and running them on AppVeyor CI.

appveyor.yml

@@ -39,7 +39,7 @@ install: git submodule update --init
 
 before_build:
 - ps: |
-    $env:PATH = $env:PATH -replace "C:\\Program Files \(x86\)\\Git\\bin",""
+    $env:PATH = $env:PATH -replace "C:\\Program Files\\Git\\usr\\bin",""
     if (($env:compiler -ne "msys2") -and ($env:compiler -ne "cygwin")) {
       gc include\wx\msw\setup0.h |
       %{$_ -replace "define wxUSE_STL 0", "define wxUSE_STL $env:wxUSE_STL"} |
@@ -50,6 +50,6 @@ before_build:
         Where-Object pullRequestId -eq $env:APPVEYOR_PULL_REQUEST_NUMBER)[0].buildNumber) { `
         throw "There are newer queued builds for this pull request, failing early." }
 
-build_script: build\tools\appveyor.bat
+build_script: c:\projects\wxwidgets\build\tools\appveyor.bat
 
-test: off
+test_script: c:\projects\wxwidgets\build\tools\appveyor-test.bat