strbuf: add and use strbuf_insertstr()

Add a function for inserting a C string into a strbuf.  Use it
throughout the source to get rid of magic string length constants and
explicit strlen() calls.

Like strbuf_addstr(), implement it as an inline function to avoid the
implicit strlen() calls to cause runtime overhead.

Helped-by: Taylor Blau <me@ttaylorr.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.h

@@ -244,6 +244,18 @@ void strbuf_addchars(struct strbuf *sb, int c, size_t n);
  */
 void strbuf_insert(struct strbuf *sb, size_t pos, const void *, size_t);
 
+/**
+ * Insert a NUL-terminated string to the given position of the buffer.
+ * The remaining contents will be shifted, not overwritten.  It's an
+ * inline function to allow the compiler to resolve strlen() calls on
+ * constants at compile time.
+ */
+static inline void strbuf_insertstr(struct strbuf *sb, size_t pos,
+				    const char *s)
+{
+	strbuf_insert(sb, pos, s, strlen(s));
+}
+
 /**
  * Insert data to the given position of the buffer giving a printf format
  * string. The contents will be shifted, not overwritten.