move odb_* declarations out of git-compat-util.h

These functions were originally conceived as wrapper
functions similar to xmkstemp(). They were later moved by
463db9b (wrapper: move odb_* to environment.c,
2010-11-06). The more appropriate place for a declaration is
in cache.h.

While we're at it, let's add some basic docstrings.

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

Author: peff

cache.h

@@ -1563,6 +1563,18 @@ extern struct packed_git *find_sha1_pack(const unsigned char *sha1,
 
 extern void pack_report(void);
 
+/*
+ * Create a temporary file rooted in the object database directory.
+ */
+extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
+
+/*
+ * Create a pack .keep file in the object database's pack directory, for
+ * a pack with checksum "sha1". The return value is a file descriptor opened
+ * for writing, or -1 on error. The name of the keep file is written to "name".
+ */
+extern int odb_pack_keep(char *name, size_t namesz, const unsigned char *sha1);
+
 /*
  * mmap the index file for the specified packfile (if it is not
  * already mmapped).  Return 0 on success.

git-compat-util.h

@@ -803,8 +803,6 @@ extern FILE *xfopen(const char *path, const char *mode);
 extern FILE *xfdopen(int fd, const char *mode);
 extern int xmkstemp(char *template);
 extern int xmkstemp_mode(char *template, int mode);
-extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
-extern int odb_pack_keep(char *name, size_t namesz, const unsigned char *sha1);
 extern char *xgetcwd(void);
 extern FILE *fopen_for_writing(const char *path);