Calls to std::tolower/toupper should cast their argument to an unsigned char.

[SVN r28504]

libs/regex

@@ -1 +1 @@
-Subproject commit ed93c55832072b4ae6275a796605b3d888e4c3a1
+Subproject commit b04bc5b5b07762c8e7f981f8f5aca3c087714bd1