Intelligent avoid of files re-download

[Lucioric2000]

Hi. I introduced some changes in the Java code to avoid re-download of files.

[julie-sullivan]

https://www.gnu.org/software/wget/manual/wget.html#Time_002dStamping

The time-stamping in GNU Wget is turned on using ‘--timestamping’ (‘-N’) option, 
or through timestamping = on directive in .wgetrc. With this option, for each file it 
intends to download, Wget will check whether a local file of the same name exists. 
If it does, and the remote file is not newer, Wget will not download it.

[Lucioric2000]

https://www.gnu.org/software/wget/manual/wget.html#Time_002dStamping

The time-stamping in GNU Wget is turned on using ‘--timestamping’ (‘-N’) option, 
or through timestamping = on directive in .wgetrc. With this option, for each file it 
intends to download, Wget will check whether a local file of the same name exists. 
If it does, and the remote file is not newer, Wget will not download it.

Yeah. What I added is that after filenane and timestamp comparison, it compares file size, and if the file is smaller in the destination, it assumes that it is a broken download, and downloads the remainder of the bytes.