[PATCH] quote.h: simplify the inclusion

Attempting to include quote.h without first including strbuf.h results
in warnings:

 ./quote.h:33:33: warning: ‘struct strbuf’ declared inside parameter list
 ./quote.h:33:33: warning: its scope is only this definition or declaration, which is probably not what you want
 ./quote.h:34:34: warning: ‘struct strbuf’ declared inside parameter list
 ...

Add a toplevel declaration for struct strbuf to avoid this.

While at it, stop including system headers from quote.h.  git source
files already need to include git-compat-util.h sooner to ensure the
appropriate feature test macros are defined.

Signed-off-by: Jonathan Nieder <redacted>
---
Noticed while trying to use quote.h in a source file without strbufs.

 quote.h |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/quote.h b/quote.h
index 38003bf..024e21d 100644
--- a/quote.h
+++ b/quote.h

@@ -1,8 +1,7 @@
 #ifndef QUOTE_H
 #define QUOTE_H
 
-#include <stddef.h>
-#include <stdio.h>
+struct strbuf;
 
 /* Help to copy the thing properly quoted for the shell safety.
  * any single quote is replaced with '\'', any exclamation point

-- 
1.7.4.rc0