Move everything syntax-related to syntax/, break deps on rest of compiler

src/comp/syntax is currently just a sub-module of rustc, but it will,
in the near future, be its own crate. This includes:

 - The AST data structure
 - The parser
 - The pretty-printer
 - Visit, walk, and fold
 - The syntax extension system
 - Some utility stuff that should be in the stdlib*

*) Stdlib extensions currently require a snapshot before they can be
   used, and the win build is very broken right now. This is temporary
   and will be cleaned up when one of those problems goes away.

A lot of code was moved by this patch, mostly towards a more organized
layout. Some package paths did get longer, and I guess the new layout
will take some getting used to. Sorry about that!

Please try not to re-introduce any dependencies in syntax/ on any of
the other src/comp/ subdirs.

src/comp/syntax/codemap.rs

@@ -0,0 +1,96 @@
+
+import std::vec;
+import std::term;
+import std::io;
+import std::option;
+import std::option::some;
+import std::option::none;
+
+type filename = str;
+
+/* A codemap is a thing that maps uints to file/line/column positions
+ * in a crate. This to make it possible to represent the positions
+ * with single-word things, rather than passing records all over the
+ * compiler.
+ */
+type filemap = @rec(filename name, uint start_pos, mutable vec[uint] lines);
+
+type codemap = @rec(mutable vec[filemap] files);
+
+type loc = rec(filename filename, uint line, uint col);
+
+fn new_codemap() -> codemap {
+    let vec[filemap] files = [];
+    ret @rec(mutable files=files);
+}
+
+fn new_filemap(filename filename, uint start_pos) -> filemap {
+    ret @rec(name=filename, start_pos=start_pos, mutable lines=[0u]);
+}
+
+fn next_line(filemap file, uint pos) { vec::push[uint](file.lines, pos); }
+
+fn lookup_pos(codemap map, uint pos) -> loc {
+    auto a = 0u;
+    auto b = vec::len[filemap](map.files);
+    while (b - a > 1u) {
+        auto m = (a + b) / 2u;
+        if (map.files.(m).start_pos > pos) { b = m; } else { a = m; }
+    }
+    auto f = map.files.(a);
+    a = 0u;
+    b = vec::len[uint](f.lines);
+    while (b - a > 1u) {
+        auto m = (a + b) / 2u;
+        if (f.lines.(m) > pos) { b = m; } else { a = m; }
+    }
+    ret rec(filename=f.name, line=a + 1u, col=pos - f.lines.(a));
+}
+
+type span = rec(uint lo, uint hi);
+
+fn span_to_str(&span sp, &codemap cm) -> str {
+    auto lo = lookup_pos(cm, sp.lo);
+    auto hi = lookup_pos(cm, sp.hi);
+    ret #fmt("%s:%u:%u:%u:%u", lo.filename, lo.line, lo.col, hi.line, hi.col);
+}
+
+fn emit_diagnostic(&option::t[span] sp, &str msg, &str kind, u8 color,
+                   &codemap cm) {
+    auto ss = "<input>:0:0:0:0";
+    alt (sp) {
+        case (some(?ssp)) { ss = span_to_str(ssp, cm); }
+        case (none) { }
+    }
+    io::stdout().write_str(ss + ": ");
+    if (term::color_supported()) {
+        term::fg(io::stdout().get_buf_writer(), color);
+    }
+    io::stdout().write_str(#fmt("%s:", kind));
+    if (term::color_supported()) {
+        term::reset(io::stdout().get_buf_writer());
+    }
+    io::stdout().write_str(#fmt(" %s\n", msg));
+}
+
+fn emit_warning(&option::t[span] sp, &str msg, &codemap cm) {
+    emit_diagnostic(sp, msg, "warning", 11u8, cm);
+}
+fn emit_error(&option::t[span] sp, &str msg, &codemap cm) {
+    emit_diagnostic(sp, msg, "error", 9u8, cm);
+}
+fn emit_note(&option::t[span] sp, &str msg, &codemap cm) {
+    emit_diagnostic(sp, msg, "note", 10u8, cm);
+}
+
+
+//
+// Local Variables:
+// mode: rust
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+//