case-insensitive URI scheme comparison

Required according to RFC 3986:

> An implementation should accept uppercase letters as equivalent to
> lowercase in scheme names

Closes #330

src/input/plugins/AlsaInputPlugin.cxx

@@ -33,7 +33,7 @@
 #include "util/RuntimeError.hxx"
 #include "util/StringCompare.hxx"
 #include "util/ReusableArray.hxx"
-
+#include "util/ASCII.hxx"
 #include "Log.hxx"
 #include "event/MultiSocketMonitor.hxx"
 #include "event/DeferredMonitor.hxx"
@@ -147,7 +147,7 @@ private:
 inline InputStream *
 AlsaInputStream::Create(const char *uri, Mutex &mutex, Cond &cond)
 {
-	const char *device = StringAfterPrefix(uri, "alsa://");
+	const char *device = StringAfterPrefixCaseASCII(uri, "alsa://");
 	if (device == nullptr)
 		return nullptr;