Trim 0b/0o/0x prefixes when parsing numbers.

[cuiwc]

In some rare cases, the file mode field in the headers of an ar package could have "0o" as prefix since the radix is 8. This change tries to trim radix prefixes when parsing numbers, as the current Rust from_str_radix API doesn't parse radix prefixes yet (refer to rust-lang/rfcs#1098).

[mdsteele]

Could you add new unit test(s) for this?

[mdsteele]

Also, out of curiosity, do you have any examples of archive files/tools in the wild that use such a prefix?

[cuiwc]

Thanks, @mdsteele.

Added a test with entry having "0o" prefix in the file mode field. Passed cargo fmt and cargo test verifications.

I ran across this issue with a VMware vSphere Installation Bundle (Vib) file, which is basically an ar archive but with file mode set to 0o0:

$ file VMW_bootbank_content.vib
VMW_bootbank_content.vib: current ar archive

$ head -c 100 VMW_bootbank_content.vib
!<arch>
descriptor.xml  0           0     0     0o0     3747      `
<vib version="5.0"><type>bootban%

The number parser returns "Invalid file mode field in entry header" error for this field. The ar program can extract this archive successfully.

[mdsteele]

Thanks!