Add wxCheckOsVersion() to implement platform based OS version checks.

Windows implements VerifyVersionInfo api since Win2k. Starting with Windows 8.1 GetVersionEx is deprecated and may not return the expected version number if the application does not contain the correct compatibility information in its manifest. VerifyVersionInfo works independent of manifest in the executable (and is the recommend way to check).

Existing code may already use wxPlatformInfo::CheckOSVersion() so the method forwards the call to wxCheckOsVersion if initialized for the current system.

src/common/platinfo.cpp

@@ -135,6 +135,8 @@ wxPlatformInfo::wxPlatformInfo(wxPortId pid, int tkMajor, int tkMinor,
                                wxEndianness endian,
                                bool usingUniversal)
 {
+    m_initializedForCurrentPlatform = false;
+
     m_tkVersionMajor = tkMajor;
     m_tkVersionMinor = tkMinor;
     m_port = pid;
@@ -166,6 +168,8 @@ bool wxPlatformInfo::operator==(const wxPlatformInfo &t) const
 
 void wxPlatformInfo::InitForCurrentPlatform()
 {
+    m_initializedForCurrentPlatform = true;
+
     // autodetect all informations
     const wxAppTraits * const traits = wxTheApp ? wxTheApp->GetTraits() : NULL;
     if ( !traits )
@@ -294,6 +298,19 @@ wxString wxPlatformInfo::GetEndiannessName(wxEndianness end)
     return wxEndiannessNames[end];
 }
 
+bool wxPlatformInfo::CheckOSVersion(int major, int minor) const
+{
+    // If this instance of wxPlatformInfo has been initialized by InitForCurrentPlatform()
+    // this check gets forwarded to the wxCheckOsVersion which might do more than a simple
+    // number check if supported by the platform
+    if (m_initializedForCurrentPlatform)
+        return wxCheckOsVersion(major, minor);
+    else
+        return DoCheckVersion(GetOSMajorVersion(),
+                            GetOSMinorVersion(),
+                            major,
+                            minor);
+}
 
 // ----------------------------------------------------------------------------
 // wxPlatformInfo - string -> enum conversions