Check content before zip/unzip the txhashset (#1174)

* Check txhashset content before zip/unzip
* Add header in txhashset verification
* Add copy function and test
* Add file util
* Now check and remove unexpected files instead of just crashing

store/src/pmmr.rs

@@ -31,6 +31,14 @@ const PMMR_DATA_FILE: &'static str = "pmmr_data.bin";
 const PMMR_LEAF_FILE: &'static str = "pmmr_leaf.bin";
 const PMMR_PRUN_FILE: &'static str = "pmmr_prun.bin";
 
+/// The list of PMMR_Files for internal purposes
+pub const PMMR_FILES: [&str; 4] = [
+	PMMR_HASH_FILE,
+	PMMR_DATA_FILE,
+	PMMR_LEAF_FILE,
+	PMMR_PRUN_FILE,
+];
+
 /// PMMR persistent backend implementation. Relies on multiple facilities to
 /// handle writing, reading and pruning.
 ///