Move more functions into the new gtkmisc.c.

Several utility functions I've written over the last few weeks were in
rather random places because I didn't have a central gtkmisc.c to put
them in. Now I've got one, put them there!

unix/gtkmisc.h

@@ -5,6 +5,11 @@
 #ifndef PUTTY_GTKMISC_H
 #define PUTTY_GTKMISC_H
 
+int string_width(const char *text);
+void get_label_text_dimensions(const char *text, int *width, int *height);
+
+void align_label_left(GtkLabel *label);
+
 GtkWidget *our_dialog_new(void);
 void our_dialog_add_to_content_area(GtkWindow *dlg, GtkWidget *w,
                                     gboolean expand, gboolean fill,