Change how GF deals with character encodings in grammar files

1. The default encoding is changed from Latin-1 to UTF-8.

2. Alternate encodings should be specified as "--# -coding=enc", the old
   "flags coding=enc" declarations have no effect but are still checked for
   consistency.

3. A transitional warning is generated for files that contain non-ASCII
   characters without specifying a character encoding:

	"Warning: default encoding has changed from Latin-1 to UTF-8"

4. Conversion to Unicode is now done *before* lexing. This makes it possible
   to allow arbitrary Unicode characters in identifiers. But identifiers are
   still stored as ByteStrings, so they are limited to Latin-1 characters
   for now.

5. Lexer.hs is no longer part of the repository. We now generate the lexer
   from Lexer.x with alex>=3. Some workarounds for bugs in alex-3.0 were
   needed. These bugs might already be fixed in newer versions of alex, but
   we should be compatible with what is shipped in the Haskell Platform.

gf.cabal

@@ -1,5 +1,5 @@
 name: gf
-version: 3.5-darcs
+version: 3.5.11-darcs
 
 cabal-version: >= 1.8
 build-type: Custom
@@ -140,8 +140,8 @@ Executable gf
   if flag(new-comp)
     cpp-options: -DNEW_COMP
 
-  build-tools: happy
-           --, alex>=2 && <3 -- tricky to install in Ubuntu 12.04
+  build-tools: happy, alex>=3
+
   if os(windows)
     build-depends: Win32
   else