Maintenance release for 2.51 branch

Highlights

• Updated bundled Git to 2.16.2
• Updated Putty to 0.70

Features:

• TaskCanceledException for ShowSelectedFileDiff() - Issue 4570
• Add a hotkey for toggling viewing of Tags - Issue 4449
• Fixes on jira commit hint plugin - PR 4412
• Add two ScriptEvents, BeforeMerge, AfterMerge - Issue 4380
• Better display of "Find and replace" dialog on multiple screens computer - PR 4354
• Commit "Author" text box has incorrect descriptive text - Issue 3501
• Keep last used Destination in clone dialog as entered - Issue 2313

Fixes:

• Wrong diff for initial commit - Issue 4580
• Find in the Diff tab shows differences reversed after wrapping around the files - Issue 4546
• "Restore to selected version" function is removed from 2.51 - Issue 4535
• Update Git for Windows version to account for recent GitHub breakage 4523
• GitK is not launched with newer Git - Issue 4510
• PuTTY Installer Is Outdated - Issue 4509
• GitEx selects the top revision after creating a new tag - Issue 4495
• 2.51: App crashes upon pressing "Script" - Issue 4488
• Find in the Diff tab fails to find text - Issue 4485
• Branch input isn't focused on Merge window - Issue 4464
• Option to set language in - Dictionary For Spelling Check - not working - Issue 4443
• Remotes not persisted - Issue 4441
• git log is called for artificial commits - Issue 4361
• "Reword Commit" doesn't refresh the UI - Issue 3935
• Not able to issue "git flow release publish" in git-flow plugin - Issue 2838
• Fields order in "create tag" window - Issue 2515
• Submodule dialog: "Name" textbox too small for long names - Issue 1858