This moves the hardcoded "/usr/bin/vi" to a (overridable) define.  This
is mostly for -portable, so packages on other systems can provide a
different path (I'm thinking in particular of NixOS where in /usr/ there
is only /usr/bin/env and all the "usual" paths are otherwise absent.)

We do the same for the other programs (ssh, ssh-keygen, signify).

As side-effect I'll be able to switch back to ed locally, too :)

ok?

diff /home/op/w/got
commit - c5d61cbc3a9c337b669af6b330709b6b4d43c872
path + /home/op/w/got
blob - 395b21d6bf1ba81c76d54f3c0c75a094440ca583
file + cvg/cvg.c
--- cvg/cvg.c
+++ cvg/cvg.c
@@ -69,6 +69,10 @@
 #define nitems(_a)	(sizeof((_a)) / sizeof((_a)[0]))
 #endif
 
+#ifndef GOT_DEFAULT_EDITOR
+#define GOT_DEFAULT_EDITOR "/usr/bin/vi"
+#endif
+
 static volatile sig_atomic_t sigint_received;
 static volatile sig_atomic_t sigpipe_received;
 
@@ -281,7 +285,7 @@ get_editor(char **abspath)
 	}
 
 	if (*abspath == NULL) {
-		*abspath = strdup("/usr/bin/vi");
+		*abspath = strdup(GOT_DEFAULT_EDITOR);
 		if (*abspath == NULL)
 			return got_error_from_errno("strdup");
 	}
blob - 488dc79c339ccc7d9f24681ea94bbf19ab7b4309
file + got/got.c
--- got/got.c
+++ got/got.c
@@ -68,6 +68,10 @@
 #define nitems(_a)	(sizeof((_a)) / sizeof((_a)[0]))
 #endif
 
+#ifndef GOT_DEFAULT_EDITOR
+#define GOT_DEFAULT_EDITOR "/usr/bin/vi"
+#endif
+
 static volatile sig_atomic_t sigint_received;
 static volatile sig_atomic_t sigpipe_received;
 
@@ -310,7 +314,7 @@ get_editor(char **abspath)
 	}
 
 	if (*abspath == NULL) {
-		*abspath = strdup("/usr/bin/vi");
+		*abspath = strdup(GOT_DEFAULT_EDITOR);
 		if (*abspath == NULL)
 			return got_error_from_errno("strdup");
 	}