Refactor the key-components mechanism a bit.

Having recently pulled it out into its own file, I think it could also
do with a bit of tidying. In this rework:

 - the substructure for a single component now has a globally visible
   struct tag, so you can make a variable pointing at it, saving
   verbiage in every piece of code looping over a key_components

 - the 'is_mp_int' flag has been replaced with a type enum, so that
   more types can be added without further upheaval

 - the printing loop in cmdgen.c for puttygen --dump has factored out
   the initial 'name=' prefix on each line so that it isn't repeated
   per component type

 - the storage format for text components is now a strbuf rather than
   a plain char *, which I think is generally more useful.

1 files changed, 12 insertions, 8 deletions

diff --git a/ssh.h b/ssh.h
index cb26b74b..e0c45091 100644
--- a/ssh.h
+++ b/ssh.h
@@ -542,16 +542,20 @@ struct eddsa_key {
 WeierstrassPoint *ecdsa_public(mp_int *private_key, const ssh_keyalg *alg);
 EdwardsPoint *eddsa_public(mp_int *private_key, const ssh_keyalg *alg);
 
+typedef enum KeyComponentType {
+    KCT_TEXT, KCT_MPINT
+} KeyComponentType;
+typedef struct key_component {
+    char *name;
+    KeyComponentType type;
+    union {
+        strbuf *str;                   /* used for KCT_TEXT */
+        mp_int *mp;                    /* used for KCT_MPINT */
+    };
+} key_component;
 typedef struct key_components {
     size_t ncomponents, componentsize;
-    struct {
-        char *name;
-        bool is_mp_int;
-        union {
-            char *text;
-            mp_int *mp;
-        };
-    } *components;
+    key_component *components;
 } key_components;
 key_components *key_components_new(void);
 void key_components_add_text(key_components *kc,