fixes to edify and updater script

A few more changes to edify:

  - fix write_raw_image(); my last change neglected to close the write
    context, so the written image was corrupt.

  - each expression tracks the span of the source code from which it
    was compiled, so that assert()'s error message can include the
    source of the expression that failed.

  - the 'cookie' argument to each Function is replaced with a State
    object, which contains the cookie, the source script (for use with
    the above spans), and the current error message (replacing the
    global variables that were used for this purpose).

  - in the recovery image, a new command "ui_print" can be sent back
    through the command pipe to cause text to appear on the screen.
    Add a new ui_print() function to print things from scripts.
    Rename existing "print" function to "stdout".
diff --git a/edify/parser.y b/edify/parser.y
index cf163c0..3f9ade1 100644
--- a/edify/parser.y
+++ b/edify/parser.y
@@ -20,6 +20,7 @@
 #include <string.h>
 
 #include "expr.h"
+#include "yydefs.h"
 #include "parser.h"
 
 extern int gLine;
@@ -30,6 +31,8 @@
 
 %}
 
+%locations
+
 %union {
     char* str;
     Expr* expr;
@@ -68,19 +71,21 @@
     $$->name = $1;
     $$->argc = 0;
     $$->argv = NULL;
+    $$->start = @$.start;
+    $$->end = @$.end;
 }
-|  '(' expr ')'                      { $$ = $2; }
-|  expr ';'                          { $$ = $1; }
-|  expr ';' expr                     { $$ = Build(SequenceFn, 2, $1, $3); }
-|  error ';' expr                    { $$ = $3; }
-|  expr '+' expr                     { $$ = Build(ConcatFn, 2, $1, $3); }
-|  expr EQ expr                      { $$ = Build(EqualityFn, 2, $1, $3); }
-|  expr NE expr                      { $$ = Build(InequalityFn, 2, $1, $3); }
-|  expr AND expr                     { $$ = Build(LogicalAndFn, 2, $1, $3); }
-|  expr OR expr                      { $$ = Build(LogicalOrFn, 2, $1, $3); }
-|  '!' expr                          { $$ = Build(LogicalNotFn, 1, $2); }
-|  IF expr THEN expr ENDIF           { $$ = Build(IfElseFn, 2, $2, $4); }
-|  IF expr THEN expr ELSE expr ENDIF { $$ = Build(IfElseFn, 3, $2, $4, $6); }
+|  '(' expr ')'                      { $$ = $2; $$->start=@$.start; $$->end=@$.end; }
+|  expr ';'                          { $$ = $1; $$->start=@1.start; $$->end=@1.end; }
+|  expr ';' expr                     { $$ = Build(SequenceFn, @$, 2, $1, $3); }
+|  error ';' expr                    { $$ = $3; $$->start=@$.start; $$->end=@$.end; }
+|  expr '+' expr                     { $$ = Build(ConcatFn, @$, 2, $1, $3); }
+|  expr EQ expr                      { $$ = Build(EqualityFn, @$, 2, $1, $3); }
+|  expr NE expr                      { $$ = Build(InequalityFn, @$, 2, $1, $3); }
+|  expr AND expr                     { $$ = Build(LogicalAndFn, @$, 2, $1, $3); }
+|  expr OR expr                      { $$ = Build(LogicalOrFn, @$, 2, $1, $3); }
+|  '!' expr                          { $$ = Build(LogicalNotFn, @$, 1, $2); }
+|  IF expr THEN expr ENDIF           { $$ = Build(IfElseFn, @$, 2, $2, $4); }
+|  IF expr THEN expr ELSE expr ENDIF { $$ = Build(IfElseFn, @$, 3, $2, $4, $6); }
 | STRING '(' arglist ')' {
     $$ = malloc(sizeof(Expr));
     $$->fn = FindFunction($1);
@@ -93,6 +98,8 @@
     $$->name = $1;
     $$->argc = $3.argc;
     $$->argv = $3.argv;
+    $$->start = @$.start;
+    $$->end = @$.end;
 }
 ;