path ops -- use standard max, min, double-is-nan

fix a comment or two as well
Review URL: https://codereview.chromium.org/13934009

git-svn-id: http://skia.googlecode.com/svn/trunk@8822 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkTypes.h b/include/core/SkTypes.h
index ae27089..4f6788c 100644
--- a/include/core/SkTypes.h
+++ b/include/core/SkTypes.h
@@ -314,6 +314,14 @@
     return a;
 }
 
+template <typename T> const T& SkTMin(const T& a, const T& b) {
+    return (a < b) ? a : b;
+}
+
+template <typename T> const T& SkTMax(const T& a, const T& b) {
+    return (b < a) ? a : b;
+}
+
 static inline int32_t SkSign32(int32_t a) {
     return (a >> 31) | ((unsigned) -a >> 31);
 }