xbps-query(8: added --cat=FILE mode support.

- This mode prints to stdout the matching FILE stored in a binary package.
- ABI break: renamed xbps_get_pkg_plist_from_binpkg() xbps_binpkg_get_plist().
- Added xbps_binpkg_get_file() as a generic way to get pkg file contents.
- Removed useless comments from xbps_api_impl.h.

lib/archive.c

@@ -31,10 +31,9 @@
 
 #include "xbps_api_impl.h"
 
-xbps_dictionary_t HIDDEN
-xbps_archive_get_dictionary(struct archive *ar, struct archive_entry *entry)
+char HIDDEN *
+xbps_archive_get_file(struct archive *ar, struct archive_entry *entry)
 {
-	xbps_dictionary_t d = NULL;
 	size_t buflen;
 	ssize_t nbytes = -1;
 	char *buf;
@@ -43,7 +42,7 @@ xbps_archive_get_dictionary(struct archive *ar, struct archive_entry *entry)
 	assert(entry != NULL);
 
 	buflen = (size_t)archive_entry_size(entry);
-	buf = malloc(buflen);
+	buf = malloc(buflen+1);
 	if (buf == NULL)
 		return NULL;
 
@@ -52,14 +51,23 @@ xbps_archive_get_dictionary(struct archive *ar, struct archive_entry *entry)
 		free(buf);
 		return NULL;
 	}
+	buf[buflen] = '\0';
+	return buf;
+}
+
+xbps_dictionary_t HIDDEN
+xbps_archive_get_dictionary(struct archive *ar, struct archive_entry *entry)
+{
+	xbps_dictionary_t d = NULL;
+	char *buf;
+
+	if ((buf = xbps_archive_get_file(ar, entry)) == NULL)
+		return NULL;
 
 	/* If blob is already a dictionary we are done */
 	d = xbps_dictionary_internalize(buf);
-	if (xbps_object_type(d) == XBPS_TYPE_DICTIONARY) {
-		free(buf);
-		return d;
-	}
-	return NULL;
+	free(buf);
+	return d;
 }
 
 int