Make module manifest v2 compatible

[theaquamarine]

The RootModule key was renamed from ModuleToProcess in PowerShell v3
so is not compatible with PowerShell v2. ModuleToProcess still exists
as an alias, so use that instead.

See discussion in #242

[shiftkey]

Just tested this out on a Win7 VM with PowerShell v2:

C:\Users\shiftkey\Documents\GitHub\posh-gitPS>git checkout v2manifest
Switched to branch 'v2manifest'
Your branch is up-to-date with 'theaquamarine/v2manifest'.
C:\Users\shiftkey\Documents\GitHub\posh-gitPS>.\install
Adding posh-git to profile...
posh-git sucessfully installed!
Please reload your profile for the changes to take effect:
. $PROFILE
C:\Users\shiftkey\Documents\GitHub\posh-gitPS>. $PROFILE
WARNING: posh-git support for PowerShell 2.0 is deprecated; you have version 2.0.
To download version 3.0, please visit https://www.microsoft.com/en-us/download/details.aspx?id=34595
For more information and to discuss this, please visit #163
To suppress this warning, change your profile to include 'Import-Module posh-git -Args $true'.
C:\Users\shiftkey\Documents\GitHub\posh-git [v2manifest ≡]>

And this is what I currently get on master when I do the same:

PS C:\Users\shiftkey\Documents\GitHub\posh-git> .\install.ps1
Adding posh-git to profile...
posh-git sucessfully installed!
Please reload your profile for the changes to take effect:
. $PROFILE
PS C:\Users\shiftkey\Documents\GitHub\posh-git> . $PROFILE
Import-Module : The 'C:\Users\shiftkey\Documents\GitHub\posh-git\posh-git.psd1' module cannot be imported because its manifest contains one or more members that are not valid. The valid manifest members are ('ModuleToProcess', 'NestedModules', 'GUID', 'Author', 'CompanyName', 'Copyright', 'ModuleVersion', 'Description', 'PowerShellVersion', 'PowerShellHostName', 'PowerShellHostVersion', 'CLRVersion', 'DotNetFrameworkVersion', 'ProcessorArchitecture', 'RequiredModules', 'TypesToProcess', 'FormatsToProcess', 'ScriptsToProcess', 'PrivateData', 'RequiredAssemblies', 'ModuleList', 'FileList',
'FunctionsToExport', 'VariablesToExport', 'AliasesToExport', 'CmdletsToExport'). Remove the members that are not valid ('RootModule'), then try to import the module again.
At C:\Users\shiftkey\Documents\GitHub\posh-git\profile.example.ps1:4 char:14

• Import-Module <<<< .\posh-git
  • CategoryInfo : InvalidData: (C:\Users\shiftk...t\posh-git.psd1:String) [Import-Module], InvalidOperationException
  • FullyQualifiedErrorId : Modules_InvalidManifestMember,Microsoft.PowerShell.Commands.ImportModuleCommand

The term 'Start-SshAgent' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At C:\Users\shiftkey\Documents\GitHub\posh-git\profile.example.ps1:25 char:15

• Start-SshAgent <<<< -Quiet
  • CategoryInfo : ObjectNotFound: (Start-SshAgent:String) [], CommandNotFoundException
  • FullyQualifiedErrorId : CommandNotFoundException

👍 to this change, will test some other OSes as well while I'm in here...

[dahlbyk]

I'll defer to @shiftkey's test matrix on this.

[shiftkey]

I'll wrap this up today, haven't found any shockers so far

[dahlbyk]

Is this the only PowerShell 2 incompatibility you've seen so far?

[dahlbyk]

N.B. New-ModuleManfest docs for -RootModule document the alias.

Note: In Windows PowerShell 2.0, this key was called "ModuleToProcess." You can use the "RootModule" parameter name or its "ModuleToProcess" alias.

I'm going to go ahead and merge. Please open another issue if you find other ways we could be less PS2-hostile.