open ifstream in zstr as binary always

[svigerske]

Sorry that things come in small pieces.
I had problems reading compressed input on Windows with zstr. (There was an exception from std::string thrown.)

Turned out that this is due to mateidavid/zstr#15, i.e., not opening the input stream as binary. On Windows, there are some conversions of carriage-return (\r) happening in that case that cause trouble.

This PR changes the zstr library to always open the input stream in binary form.
As far as I understand zstr/issues#15, this means that \r in the input are not converted away.
Fortunately, your LP and MPS readers seem to handle this case:

• In the fixed-form MPS reader, deleting trailing whitespace includes removing \r, because isspace('\r') is true: https://github.com/ERGO-Code/HiGHS/blob/master/src/io/HMPSIO.cpp#L474-L484
• In the free-form MPS reader, you use your own trim() function to remove white-space, which includes \r: https://github.com/ERGO-Code/HiGHS/blob/master/src/util/stringutil.h#L27
• In the LP reader, there is an explicit check for \r: https://github.com/ERGO-Code/HiGHS/blob/master/extern/filereaderlp/reader.cpp#L898-L900

[svigerske]

Of course it had to fail on mac now.

PS: Changed to open in binary mode only if windows.

[jajhall]

Thanks