Open the TortoiseSVN or TortoiseGit Commit dialog (as appropriate) showing all modified files in a Visual Studio solution by running Tortoise-CommitSolution in the Package Manager Console.

commit.ps1

# Tortoise-CommitSolution by Adam Coyne <adam@coyne.nu>
# Edit your NuGet PowerShell profile ($Env:UserProfile\Documents\WindowsPowerShell\NuGet_profile.ps1) to source this file (like ". $Env:UserProfile\Documents\WindowsPowerShell\commit.ps1") and add a convenient alias (like "Set-Alias commit Tortoise-CommitSolution")
function Tortoise-CommitSolution {
    [string[]]$projectpaths = Get-Project -All | foreach { [System.IO.Path]::GetDirectoryName($_.FullName) }
    $projectpaths += $dte.Solution.FullName
    if($projectpaths.length -gt 0) {
        $filename = Write-PathFile(Filter-PathArray($projectpaths))
        # Visual Studio is 32-bit, but I have 64-bit TortoiseSvn and TortoiseGit installed
        $programfiles = $Env:ProgramW6432
        if(!$programfiles) { $programfiles = $Env:ProgramFiles }
        if(Get-LocalOrParentPath .svn $projectpaths[0]) {
            & "$programfiles\TortoiseSVN\bin\tortoiseproc.exe" /command:commit /deletepathfile /pathfile:`"$filename`" /hwnd:$($dte.MainWindow.HWnd)
        } elseif(Get-LocalOrParentPath .git $projectpaths[0]) {
            & "$programfiles\TortoiseGit\bin\tortoisegitproc.exe" /command:commit /deletepathfile /pathfile:`"$filename`" /hwnd:$($dte.MainWindow.HWnd)
        }        
    }
}

# Filter out paths that are contained within another path, so modified files won't show up twice in the Commit dialog.
function Filter-PathArray([string[]]$paths) {
    [string[]]$filteredprojectpaths = @()
    [string]$lastCommonParentPath = "*" # an initial value that won't match

    foreach($p in $paths | Sort-Object) {
        if(-not $p.StartsWith($lastCommonParentPath)) {
            $filteredprojectpaths += $p
            $lastCommonParentPath = $p + "\"
        }
    }
    return $filteredprojectpaths
}

# Tortoise's pathfile contains paths delimited by line feeds and with a trailing line feed, and is formatted as Unicode with no BOM.
function Write-PathFile([string[]]$files) {
    $filename = [System.IO.Path]::GetTempFileName()
    $contents = [string]::join("`n", $files) + "`n"
    $bytes = [System.Text.Encoding]::Unicode.GetBytes($contents)
    Set-Content -Encoding byte $filename $bytes
    return $filename
}

# From https://github.com/dahlbyk/posh-git
function Get-LocalOrParentPath($path, $startPath = '.') {
    $checkIn = Get-Item $startPath
    while ($checkIn -ne $NULL) {
        $pathToTest = [System.IO.Path]::Combine($checkIn.fullname, $path)
        if (Test-Path $pathToTest) {
            return $pathToTest
        } else {
            $checkIn = $checkIn.parent
        }
    }
    return $null
}