prompt: use git_terminal_prompt

Our custom implementation of git_terminal_prompt has many
advantages over regular getpass(), as described in the prior
commit.

This also lets us implement a PROMPT_ECHO flag for callers
who want it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

prompt.c

@@ -2,6 +2,7 @@
 #include "run-command.h"
 #include "strbuf.h"
 #include "prompt.h"
+#include "compat/terminal.h"
 
 static char *do_askpass(const char *cmd, const char *prompt)
 {
@@ -50,7 +51,7 @@ char *git_prompt(const char *prompt, int flags)
 			return do_askpass(askpass, prompt);
 	}
 
-	r = getpass(prompt);
+	r = git_terminal_prompt(prompt, flags & PROMPT_ECHO);
 	if (!r)
 		die_errno("could not read '%s'", prompt);
 	return r;

prompt.h

@@ -2,6 +2,7 @@
 #define PROMPT_H
 
 #define PROMPT_ASKPASS (1<<0)
+#define PROMPT_ECHO    (1<<1)
 
 char *git_prompt(const char *prompt, int flags);
 char *git_getpass(const char *prompt);