vcs-svn: handle log message with embedded NUL

Pass the log message by strbuf instead of as a C-style string and use
fwrite instead of printf to write it to fast-import so embedded '\0'
bytes can be preserved.

Currently "git log" doesn't show the embedded NULs but "git cat-file
commit" can.

While at it, stop including system headers from repo_tree.h.  git
source files need to include git-compat-util.h (or cache.h or
builtin.h) sooner to ensure the appropriate feature test macros are
defined.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

vcs-svn/repo_tree.c

@@ -278,8 +278,9 @@ void repo_diff(uint32_t r1, uint32_t r2)
 		    repo_commit_root_dir(commit_pointer(r2)));
 }
 
-void repo_commit(uint32_t revision, const char *author, char *log,
-		 const char *uuid, const char *url, unsigned long timestamp)
+void repo_commit(uint32_t revision, const char *author,
+		const struct strbuf *log, const char *uuid, const char *url,
+		unsigned long timestamp)
 {
 	fast_export_commit(revision, author, log, uuid, url, timestamp);
 	dent_commit();