Making some asserts internal.

They shouldn't be triggered by the user, so no explanational message is
needed (but exact position in source is).

src/Color.h

@@ -54,8 +54,7 @@ template<class T> inline typename std::enable_if<std::is_floating_point<T>::valu
         case 3: return {p, q, value};
         case 4: return {t, p, value};
         case 5: return {value, p, q};
-        default:
-            CORRADE_ASSERT(false, "It shouldn't get here.", {});
+        default: CORRADE_INTERNAL_ASSERT(false);
     }
 }
 template<class T> inline typename std::enable_if<std::is_integral<T>::value, Color3<T>>::type fromHSV(typename Color3<T>::HSV hsv) {

src/Implementation/BufferState.cpp

@@ -62,8 +62,7 @@ std::size_t BufferState::indexForTarget(Buffer::Target target) {
         #endif
     }
 
-    CORRADE_ASSERT(false, "Unknown Buffer target", 0);
-    return 0;
+    CORRADE_INTERNAL_ASSERT(false);
 }
 
 }}

src/Shader.cpp

@@ -32,23 +32,25 @@ Shader::Shader(Version version, Type type): _type(type), _state(State::Initializ
 
     switch(version) {
         #ifndef MAGNUM_TARGET_GLES
-        case Version::GL210: addSource("#version 120\n"); break;
-        case Version::GL300: addSource("#version 130\n"); break;
-        case Version::GL310: addSource("#version 140\n"); break;
-        case Version::GL320: addSource("#version 150\n"); break;
-        case Version::GL330: addSource("#version 330\n"); break;
-        case Version::GL400: addSource("#version 400\n"); break;
-        case Version::GL410: addSource("#version 410\n"); break;
-        case Version::GL420: addSource("#version 420\n"); break;
-        case Version::GL430: addSource("#version 430\n"); break;
+        case Version::GL210: addSource("#version 120\n"); return;
+        case Version::GL300: addSource("#version 130\n"); return;
+        case Version::GL310: addSource("#version 140\n"); return;
+        case Version::GL320: addSource("#version 150\n"); return;
+        case Version::GL330: addSource("#version 330\n"); return;
+        case Version::GL400: addSource("#version 400\n"); return;
+        case Version::GL410: addSource("#version 410\n"); return;
+        case Version::GL420: addSource("#version 420\n"); return;
+        case Version::GL430: addSource("#version 430\n"); return;
         #else
-        case Version::GLES200: addSource("#version 100\n"); break;
-        case Version::GLES300: addSource("#version 300\n"); break;
+        case Version::GLES200: addSource("#version 100\n"); return;
+        case Version::GLES300: addSource("#version 300\n"); return;
         #endif
 
-        default:
-            CORRADE_ASSERT(false, "Shader::Shader(): unsupported version" << GLint(version), );
+        case Version::None:
+            CORRADE_ASSERT(false, "Shader::Shader(): unsupported version" << version, );
     }
+
+    CORRADE_INTERNAL_ASSERT(false);
 }
 
 Shader::Shader(Shader&& other): _type(other._type), _state(other._state), sources(other.sources), shader(other.shader) {