Case-sensitivity Issue on OSX

Hello,

Appreciate this ticket #685 has been closed but I'm experiencing similar behaviour on OSX.

Specifically:
- `rez-env Maya maya` results in the highest version Maya package added twice (i.e. in the resolved packages list and by checking the $PATH variable)

```
Fortran:~ jasonfairley$ rez-env Maya maya

You are now in a rez-configured environment.

resolved by jasonfairley@Fortran.local, on Wed Jul 22 18:22:15 2020, using Rez v2.62.0

requested packages:
Maya
maya
~platform==osx (implicit)
~arch==x86_64 (implicit)
~os==osx-10.14 (implicit)

resolved packages:
Maya-2020 /Users/jasonfairley/rez/packages/develop/Maya/2020/platform-osx (local)
maya-2020 /Users/jasonfairley/rez/packages/develop/maya/2020/platform-osx (local)
platform-osx /Users/jasonfairley/Google Drive/Software/packages/basic/platform/osx
> bash-3.2$
```

- `rez-env maya foo` (where `foo` requires `Maya`) results in an environment with `maya-2020` and `Maya-2020` (as above)

```
Fortran:~ jasonfairley$ rez-env maya helloWorldCmd

You are now in a rez-configured environment.

resolved by jasonfairley@Fortran.local, on Wed Jul 22 21:13:42 2020, using Rez v2.62.0

requested packages:
maya
helloWorldCmd
~platform==osx (implicit)
~arch==x86_64 (implicit)
~os==osx-10.14 (implicit)

resolved packages:
Maya-2020 /Users/jasonfairley/rez/packages/develop/Maya/2020/platform-osx (local)
arch-x86_64 /Users/jasonfairley/Google Drive/Software/packages/basic/arch/x86_64
helloWorldCmd-1.0.0 /Users/jasonfairley/rez/packages/develop/helloWorldCmd/1.0.0/platform-osx/arch-x86_64/Maya-2020 (local)
maya-2020 /Users/jasonfairley/rez/packages/develop/maya/2020/platform-osx (local)
platform-osx /Users/jasonfairley/Google Drive/Software/packages/basic/platform/osx
> bash-3.2$
```

- `rez-env maya-2019 foo` (where `foo` requires `Maya`) results in an environment with `maya-2019` and `Maya-2020` (where 2019 and 2020 are package versions of Maya) ... as well as `foo` of course.

```
Fortran:~ jasonfairley$ rez-env maya-2019 helloWorldCmd

You are now in a rez-configured environment.

resolved by jasonfairley@Fortran.local, on Wed Jul 22 21:15:13 2020, using Rez v2.62.0

requested packages:
maya-2019
helloWorldCmd
~platform==osx (implicit)
~arch==x86_64 (implicit)
~os==osx-10.14 (implicit)

resolved packages:
Maya-2020 /Users/jasonfairley/rez/packages/develop/Maya/2020/platform-osx (local)
arch-x86_64 /Users/jasonfairley/Google Drive/Software/packages/basic/arch/x86_64
helloWorldCmd-1.0.0 /Users/jasonfairley/rez/packages/develop/helloWorldCmd/1.0.0/platform-osx/arch-x86_64/Maya-2020 (local)
maya-2019 /Users/jasonfairley/rez/packages/develop/maya/2019/platform-osx (local)
platform-osx /Users/jasonfairley/Google Drive/Software/packages/basic/platform/osx
> bash-3.2$
```

I wanted to check what the expected behaviour is in the case? Should I expect Rez to be case sensitive?

Secondly, since there had been similar issues on Windows, just curious if anyone else is using Rez on OSX and experiencing what I've described above.

Many thanks for any and all pointers :-)

Jason.

Start by reproducing the three `rez-env` commands on OSX and compare how `Maya` and `maya` are resolved, including the dependency case. Trace the package-resolution entry point used by `rez-env`; done should establish the intended case-sensitivity behavior and prevent duplicate or conflicting Maya packages if case variants are meant to identify the same package.

Written by the indexing model from the issue text.